I think it highly depends on where you were raised, how old the graves are, etc. I don't step on recent graves in cemeteries, but there are churches in Italy in which you couldn't feasibly walk inside without stepping on some old abbott. Also I seem to recall the reason certain monks wanted to be buried in the aisle in the first place was because in this way people would step on them (a sort of a 'humiliation of the flesh even in death' thing, kinda kinky) so yeah.