Any competitor, preferably several, is better than a monopoly- even if they are rubbish. And Bing is NOT rubbish.
MrSavage makes some excellent points. Being optimised for Google doesn't make it a good site. Its perfectly possible to have a great site that isn't Google-friendly. If Bing is using different criteria, thats fine. Webbies will then say "that site shouldn't be top"- but on what basis. "It's not like Google" just doesn't cut it. And using keyword-in-domain shows intent, at the very least. If the site is otherwise non-spammy, why not reward that focus?
Exactly. Superiority is not required, merely parity, funding and time. Sure, inertia is a factor, but so is novelty. For new searchers, only novelty applies. And since new searchers are primarily the youth of today, rebellion against the status quo will mean at least a few will try new things.