I don't recall the Lucky 38 music being from any Fallout's past. I've been to every zone in F1 and F2 and don't recall that track. I wish I knew were it was from though, I love it's haunting 'Ghosts of the past' feel.
Also, I beg to differ. Mark Morgans music in the old Fallouts worked, but that music just doesn't work in a format like F3 and F:NV. I take it back, SOME of his songs didnt work, moments like in Nipton, and at the gate to The Strip, it worked. But as general overworld music, it was just annoying. I prefer Inon Zurs music being the ambient tracks in this game. But that is just me.
Edit: It wasn't a 'copy paste' from Oblivion. Oblivions composer was a different person, and it's tracks were more medieval and dream worldish. Fallout 3's music is very 'reminiscent of the days before' kind of feel.