They have a spell-like ability that would be the equivalent of a 1st-level spell, and they're immune to several common low-level spells by virtue of being Outsiders. This pushes them just above the LA line (that, and they probably wanted all genasi to have the same LA).
I have house-ruled all genasi to be Humanoids and have a +2 Cha, which will make them more worth the LA as well as making them good sorcerers (and if anyone should make a good sorcerer, it's a genasi or tiefling).