-webkit prefixes have basically the same effect. Apple has been constantly encouraging the use of -webkit prefixes ever since the iPhone came out. Notice all the discussion lately about other browsers having to adopt -webkit prefixes. This is necessary to compete on mobile, because of the mobile web essentially being the domain of one rendering engine.
This is, again, problem which is very common. Developers add -webkit- and forget about others like -ms-, -moz-, -o-, -kthml-, ... and most importantly the unprefixed original (if it is a prefix that is a part of some pending standard). I would love if people didn't use these prefixes at all but with W3C being so freakishly slow it would really hold the web back.
The prefixes like -moz-, -webkit-, and -o- are specifically for NOT contaminating the DOM with objects that are not standard compliant. These prefixes mark proposed features that are still in discussion for W3C standardization and they are introduced so they can be tested in practice. Once they are standardized, the prefixes can be dropped. That is exactly how it should be.
The -moz- prefix was first, and -webkit- came later.
