I agree, competition is great; it spurs innovation. But I don't see how all browsers using the same rendering engine is bad for competition. Are Safari and Chrome not competing? Are they not innovating?

Users would still have a choice of browsers, but the web would be a much better place for users, and developers/designers.

Has either Safari or Chrome fixed the known bugs in their CSS selector matching? No, because fixing those is not a priority for the core webkit developers.

Is it a good thing for designers for those bugs to be enshrined as a de-facto standard? I don't think so. The fact that other UAs don't have them might serve as pressure on webkit to fix them too. Maybe.