What accounts for the softer texture and sharper flavor of Italian ice creams?

There are several major factors that affect the texture of ice cream or gelato in the absence of stabilizers or gums:

1. Air mixed in during the churning essentially creates a foam, which is softer than a solid product would be. While this air may be only 10% by volume, it makes a huge difference in texture.
2. The churning and rapid freezing also minimizes the size of ice crystals, so the non-air phase is essentially a syrup of sugary water with emulsified milk fat, with very small ice crystals suspended in it. Since it is not solid, it is easier to cut.
3. The serving temperature for gelato I believe is traditionally warmer than the serving temperature of ice cream, which provides a softer texture (more syrup, less ice) allows the flavors to be perceived more easily as they are more aromatic at warmer temperatures.
4. The gelato may contain ingredients with alcohol, such as Franglico in a hazelnut gelato; this contributes a small anti-freeze effect. Similarly, the pectins from some fruit ingredients will also naturally interfere with ice crystal formation--but these influences are specific to a given recipe.

The lower milkfat percentage makes the flavors in the gelato more apparent, since they are not drowned out by the richness of the diary.

Technically, Gelato is not ice-cream since there is no (well, ~1%) cream fat to speak of.

The commonality with ice-cream is that they are both emulsions. In the case of the gelato, the protein in the egg yolks act as the emulsifier and through the churning process traps and keeps air. The sugar also impedes the formation of ice crystals to allow for the smooth and stretchy/creamy consistency. In a weird way, ice-cream and gelato have a lot in common with budino-cremoso/creme-caramel/flan/creme-brulee (taste your gelato batter next time). Of course, the difference being the three-way emulsion of sugar solution/ ice crystals / air for gelato and throw in fat for ice-cream.

The stabilizers and gums you see in other ice-creams are usually there as the substitute to lower the cost and achieve a similar kind of emulsion, not as much to improve texture. Xanthan and guar gum are less expensive than egg yolk and anything you can do to reduce the bunker-buster cost of cream. A carrageenan mixture has non-newtonian qualities (different viscosity at different speeds, like why ketchup gets runnier the harder you shake the bottle) this allows the ice-cream manufacturers to pump the ice-cream faster into containers, and again doesn't provide a big advantage for homemade ice-cream/gelato making.

the issue of temperature: ice crystals tend to grow in the freezer, that's why ice-creams and gelato lose quality over time. In making the ice-cream, besides the temperature, the time matters as well (as SAJ14SAJ noted) which is why the liquid nitrogen ice-cream ends up so smooth (requires serious safety precautions). From what I've been told (well, by a salesman) Italian Gelato machines run colder (and think faster) than regular ice-cream machines.

sharper taste: with the fat from the cream out of the way, the main flavor of the batter lifted by the sugar can come through easier. Our taste buds can't taste the sugar as well in lower temperatures so essentially the only thing left is the fragola or whatever flavoring is in the gelato.