Unnecessary for you, perhaps. But how would it hurt you if Rosetta were still available to those of us who want it? It wouldn't change your system - you'd never install it. But I'd like Rosetta so I could continue to use Office 2004 - I can't stomach the newer versions. And as several people have pointed out, many older printers and scanners still work perfectly fine, but their drivers have never been updated past the PPC versions.
I hope Apple will continue to make Rosetta available, or at least allow it to work if we can figure out how to load it into Lion (I'm not sure where it resides in my computer). I can still load iMovie HD into Snow Leopard, and it works, even though it's not available through Apple anymore. Come to think of it, I'm also using iTunes 8.2 in my new Snow Leopard computer. That one was a little tricky - once your music files have been loaded into itunes 9 or 10, it's a pain to go back.
I don't know - I guess I'm a sucker for older software that works better for me than the newer versions (even if they have less features).