Safari and Mobile Safari are full of -webkit- too…
I don’t get how you contradict yourself:
Of course it’s bad if a browser vendor implements a Web technology from another! The technology wasn’t discussed and approved in W3C. They can’t implement it.
If it’s implemented in Chrome and Firefox and they become the leading browsers, and then the Websites start to be only available for them, wouldn’t that force the others to implement too?
This isn’t fair and it’s one of the reasons W3C and other organizations exist.