To be honest, I don't really think it's a real WTF - I wouldn't use the code in production work (which most WTFs seem to...), and it is actually solving a problem which has not been solved elsewhere (most WTFs appear to be grossly over-coded attempts to solve problems which have already been solved).
The code in question here actually provides a border-radius according to the W3C specs. This is something which no browser does on its own.
HitScan's example of an existing solution to the perceived problem actually doesn't solve the problem. That example merely provides curved corners. What if the CSS specifically specifies corners which are 37px radius in Y and 54px radius in X ? The given example will not provide that, but my "WTF" will.
Anyhow... call it what you will, I had fun writing it, and that's all that matters ;-)