Mechanical differences between species run deeper than just what you see at char-gen and, as others have noted, may not always be the same from one campaign to the next.
And if you're pitching me that in this campaign all playable species are mechanically the same then I'd a) expect that sameness to run as deep as it has to to in fact make them all the same; this includes lore, social beliefs, action resolution (regardless of the action), and so on while at the same time b) wondering why you'd bother having different species be playable in that game in the first place.