Why are the storage instructions extremely opposite in cases of tea and coffee?

"Both are derived from plants" is leading you astray. Tea is made from leaves, so does not freeze particularly well, like many other aromatic leaves (coriander, basil, other leafy herbs) that aren't recommended for freezing.

Coffee, on the other hand, is made from beans, which are much less subject to damage from freezing. There's really not any reason why there should be any similarity between the two.

Finally, neither are recommended to keep in the fridge (mostly because of humidity) and coffee isn't particularly recommended to keep in the freezer; it would be more accurate to say that it can be done with less detriment than tea.

From the Starbucks website:

To keep coffee fresh, store it in an opaque, airtight container at room temperature. Storing coffee in the refrigerator or freezer for daily use can damage the coffee as warm, moist air condenses to the beans whenever the container is opened.

Here are some more reasons why it is not recommended to keep it in the freezer.

• Coffee is porous. It is exactly this feature that allows us to use oils and syrups to flavour coffee beans for those who enjoy gourmet flavoured coffees. For this same reason, coffee can also absorb flavours and moisture from your freezer. The absorbed moisture will deteriorate the natural goodness of your coffee and your expensive gourmet coffee beans will taste like your freezer.
• The coffee roasting process causes the beans to release their oils and essences in order to give the coffee its distinct flavour. This is the reason why your beans are shiny. These oils are more prominent on dark-roasted coffee and espresso beans and the reason why these coffees are so distinct in flavour. The process of freezing will break down these oils and destroy the natural coffee flavour. So unless you don't mind frozen-fish-flavoured coffee, you should avoid using the freezer to store your gourmet coffee beans at all costs.

It's not recommended, but it can be done to less detriment than tea would suffer. The reason it is worse with tea is covered in my first two paragraphs.

Typically, tea is made by fermenting and drying tea leaves , whereas coffee is made by roasting coffee beans, which are actually seeds

Both tea and whole bean coffee can be safely stored in the cabinet much like spices. However, once the coffee is ground, it starts to lose moisture, and therefore taste.

Alton Brown has a lot of great advice on this in "True Brew" http://www.foodnetwork.com/recipes/alton-brown/true-brew-recipe.html

The Food network advises: "Store whole roasted beans in an airtight container in a cool, dry place for up to two weeks. For longer storage, freeze whole beans, freezer-wrapped, up to three months. Since room-temperature ground coffee begins to go stale within a couple of days after it's ground, it should be refrigerated in an airtight container and can be stored up to two weeks."

(http://www.foodterms.com/encyclopedia/coffee/index.html)