Mozilla, Microsoft, and Opera are none too happy about Webkit’s prefixes becoming a sort of organic standard, especially on mobile:
Opera, along with Microsoft and Mozilla, announced at a CSS Working Group meeting that we would support some WebKit prefixes. This is because too many authors of mobile sites only use the WebKit-prefixed version, and not even the standard, unprefixed one, when it is available. This leads to a reduced user experience on Opera, Mobile Firefox and Mobile IE, which don’t receive the same shiny effects, such as transitions, gradients and the like, even if the browser supports those effects.
The problem to me seems to be one of education and tools. Authors don’t use -o prefix because they either don’t know about it, or they don’t have a significant Opera user base. Ditto the other browsers. iOS is king of the castle on mobile, and that means Safari, and that means WebKit.