"Less aggressive" is an understatement. They're very passive fish. Mine spends his time swimming around with two swordtails (they're like the Three Musketeers) and nibbling on algae (the glass, the gravel, the plants, the heater, the bogwood...) with his little "nose" twitching all the time.
The reason you see SAEs mentioned so much (aside from the fact that it's a pain to type Siamese Algae Eater three thousand times!) is that they actually
do eat algae, they stay passive, and they are frequently difficult to find. All of this as opposed to the CAEs (as F1 said), which are friendly while young, but grow to be aggressive with other community fish; which tend to stop eating algae as they get older; and which are frequently mislabeled as SAEs. The two look very similar, but there are some good web pages which show the differences. True SAEs should have a black stripe which runs the length of their bodies, from head to the fork in their tail.
http/www.petresources.net/fish/article/sae.html
http/www.aquatic-gardeners.org/cyprinid.html
Apparently SAEs can get slightly territorial with others of their own species, so you should either keep only 1 SAE or 5-6+ in a tank. Since these fish are workhorses, grow up to 6", and are not the prettiest fish around (sorry!), I think that most people tend to only keep one at a time.
-- Pamela