Why not? I actually buy various editions of the same books for various reasons.
If (ok, has you can see I'm not all that sold on the idea that e-books will actually replace p-books) e-books will be the way of the future, then surely down the road I'll want to liberate shelf space and buy some of my favourites. Until then I'll just aquire some new ones has e-books. Specially the thick, bloated, heavy ones.