Does BL2 have RPG elements like skills and levels? Or is it just grabbing new weapons? You're right at some level, both games are about killing stuff. But rightly or wrongly people seem to have strong differences of opinion about the player perspective and "RPG" elements -- often casting those games in different categories.
*wrote this before seeing Pyro's post
“Extinction is the rule. Survival is the exception.” -- Carl Sagan