baffo, who's Italian, claims that gelato is just Italian for ice cream, and even that, since ice cream was made earlier in Italy than in English-speaking countries, is actually the true name of ice cream. I don't want to get into metaphysical debates about the Platonic form of frozen dairy desserts, but I will say that though gelato and ice cream are concocted of similar ingredients (basically, cream and milk, eggs, and sugar), the end results are often surprisingly different.
One reason for the divergence is the type of flavourings used. Sure, they've both got your basic chocolate and coffee, but while ice cream tends to run to fruit flavours, gelatos are more often flavoured with typical Mediterranean ingredients like hazelnuts, cinnamon, or figs. They might contain crumbled Italian cookies as well, while ice creams feature Oreo cookies or something like that. (By the way, not all gelato is Old World. The amazing gelateria Casa Gelato in Vancouver has more gelato flavours than you can shake a stick at, ranging from traditional to plain wacky. Delicious though.)
Another difference between ice cream and gelato is the intensity of flavour: gelato tends to give a very intense jolt of the flavouring in question, probably because it contains less butterfat. Ice cream contains a higher proportion of heavy cream to milk, hence more butterfat; the fat coats the mouth and tongue and dulls the perception of taste. Also, gelato uses a higher proportion of flavouring, often with a shot of liqueur for an even stronger taste sensation. So ice cream is more about the cream, gelato the flavouring.
In addition, gelato is usually served at a slightly higher temperature than ice cream; you can spoon it easily right from when it's served. Besides giving gelato a creamier texture, it also makes the flavours stronger, because cold dulls flavour.
Finally, gelato tends to have less air churned into it than ice cream, giving it a denser texture.
My conclusion? Gelato and ice cream: same same, but different.