Why does my dough always need more water than the recipe calls for?

There are at least four likely causes that could be factors:

1. I'd say the most common problem for your issue is measurement error. If you aren't measuring flour by weight, it's nearly impossible to be consistent. And many recipe sources will assume different methods for measuring flour by volume. You could use the "spoon and level" method where you use a tablespoon or something to gradually add flour loosely to your measuring cup and then level off with a knife or straightedge. You could use the "scoop and sweep" method where you stick the entire measuring cup into the flour and sweep it against the edge of the bag or bin of flour to level it. The latter one will pack the flour more and result in more flour per cup. Or, you might not be leveling the flour at all, or shaking it off until it's roughly level. You could be packing the flour in tight or scooping it from a tightly settled bag, or you could be using flour that was loose after being poured or even put through a sifter to aerate it further.

   In any case, different volume measuring techniques can produce an error of 30% or more in flour measurement, which can make the difference between a dough that's stiff and dry vs. a dough that's so sticky you can't handle it. Most recipes that use volume measurements assume either a "spoon and level" or "scoop and sweep" method. If your source doesn't specify, try using a measurement method that won't pack the flour down as much -- which might solve your dry dough problem.

2. As already mentioned by ElendilTheTall, flours can vary significantly in terms of the amount of water they absorb. There's the issue of type: high-gluten vs. bread flour vs. "all-purpose" vs. pastry vs. cake. If you are using a high-protein/high-gluten flour like bread flour but the recipe requests all-purpose, your flour will likely absorb too much water. Similarly, some brands of flour are made from harder or softer wheats, even they are all termed "all-purpose." In the U.S., for example, King Arthur all-purpose will absorb more water than Gold Medal all-purpose, and both will absorb a lot more than "southern" all-purpose flours like White Lily. Flours in other countries may vary in their processing and content in other ways (ash content, extraction, milling size, etc.). And even flours from the same company will vary by batch, age, etc.

   In general, try using the type of flour recommended by the recipe. If that isn't working, you might consider a different brand, a "softer flour," or simply use less.

3. Kitchen environment can make a big difference, particularly temperature and humidity. Flour will absorb or lose moisture over time when stored in conditions with changing humidity. Dough will also absorb or lose moisture at different rates depending on your kitchen conditions. Thus, even if you measure flour by weight, you can sometimes see significant discrepancies from batch to batch. If you're using recipes that were designed in a place which was much more humid than your kitchen, it could explain some differences in outcome.

4. Bad recipes. It's perhaps obvious, but if you've mostly been using one or two sources for recipes, it's possible that there are consistent errors or problems. (Or, it's possible that the cookbooks/chefs/sources assume specific measuring techniques, flour types, etc. from what you're using.)

Regardless of what the problem is, if you're noticing a consistent error, then the most obvious solution is to try to quantify how big that error is, and then plan for it. For example, try reducing your flour measurement in every recipe by 10%, and see what happens. As you point out, it's often more annoying to add water to a dough than to add flour, so it's better to start out a bit moist and continue adding flour until you get the right texture.

If the error is consistent, and you can always fix it by reducing your amounts by X proportion, you've solved the issue. The alternative is to consider the various potential causes I mentioned above and see whether you can vary them until you find a solution.

Different flours have different levels of absorption. I'm in the UK, and whenever I use a US recipe for bread, I always, without fail, have to use considerably more water in order to get a proper consistency. Absorption will vary between brands and even between batches within brands. Baking with flour (especially baking bread) is part science, part art, and part experience.

I always buy King Arthur flour. I had some whole wheat flour stored out in the garage through cold and heat. It was 5 months past expiration, but it smelled OK, so I started making loaves of bread with it. Same recipe, flour, and measuring technique as always (scoop and level), but I had to add an extra 1/4 cup of water to every loaf.

I just go by feel and appearance of the dough. As much water as I can add without the dough getting too sticky (smearing around the stem of the paddle), and a smooth look, not shaggy. It's a lot easier to use a bread machine. Just watch the dough as the machine kneads. If you can tell right away that the dough is way too dry, you can add some water immediately, but don't put in the final amount until after the rest period (where the flour absorbs water), especially for whole wheat.

I guess my flour dried out a lot with temperatures in the 90's, even though the paper sacks were enclosed in plastic bags. But if you get a bread machine, you don't have to worry. It will be slimy when you first add water, but you won't feel it! You won't have to worry about figuring out the exact amount of water in advance. You just stand there and look at the dough, give it a push with your finger, and then add a tablespoon of water if needed, waiting for it to be absorbed before adding more.

I only use the machine for kneading. The dough is not always risen enough before it starts baking in a machine. I also don't like the oddly shaped loaves of a machine. You can get new old stock of bread machines on ebay rather cheaply. Somebody got one for Christmas, never used it, then cleans out the attic years later.