It's a nice idea, but in the end, you're not making it easier- you're making it more difficult on the vendors. Not a good idea, if you think about it.
The biggest problem that few people realize (even the people MAKING the distributions are on that list of people...) is that the packaging system on their pet distribution (Heh... I've got three so far... Ubuntu, Fedora, and Mandriva..) happens to be tied fairly tightly to that distribution- and that while it all works together nicely from a YUM, URPMI, or APT (or "FOO", for that matter...) repository or off their CD/DVD, once you try to pull in stuff from another distribution or from a non-source derived origin (say, GAMES...), you end up taking a chance on the things not working- or possibly messing the whole thing up badly enough that unless you know what you're doing, you're in for a reinstall.
I know, I've done this sort of thing before with Alien in the past. Not pretty.
It makes for a LOT more work than it's honestly worth, if you start thinking about it from that perspective- take a chance of fubaring their machine, or drop it in their home directory like we do and prep things THAT way. Which would YOU have?