CSS3 is a big mess! 4+ rules for making a corner round or adding a drop shadow! Preposterous! Where are the standards?!
I've been hearing a ton of that. There is something of a point here. We all like standards, no question they are a good thing for the industry. Seeing a bunch of messy/repeated code like CSS3 can produce doesn't feel like the clean happy code that standards is supposed to be all about.
But here is the deal.
The specs for these things aren't done yet. Standards move frigging slowly. Browser vendors know we want this stuff, so they don't wait for the spec, the use vendor-specific CSS attributes so we can start using/testing them now. This is good. It means they aren't sitting on their asses waiting for a slow train that answers to no one. When the spec does get finished, they can roll out support for it in the standard way much quicker.
In my opinion, it would be worse for browsers to implement the new attributes without the vendor-specific prefixes, as that would actually be abandoning standards.