Yeah, why do people say Jesus 'on the cross', instead of Jesus on the crusifix. He was crucified after all, not crossified. I think a crusifix is infact a t-shaped cross, although I'm not so sure what's derived from what when it comes to names and shapes/uses. ( a t-shape, not a T-shape )

Edit: a cross is an X, a crux is an t, we don't call it a 'Latin cross' for nothing. Our word 'cross' actually comes from a mix between the Latin 'crux' and the Greek 'stau-ros'. (by the way, when it comes to wikipedia on this, they need a clean-up. )
Still, you're right about the claim of the shape of the 'cross' and about this wikipedia seems to state popular beliefs as facts,

Cheers