The Register suggests a conspiracy -- that Apple is deliberately throttling Web Clip and WebView performance so web apps can't compete with the App Store and cut into Apple's 30% share of revenues. Of course, many web apps are free and Apple's 30% share of similarly free App Store apps is exactly zero. Likewise, lack of WebView support hurts the performance of App Store apps, not web apps. (iTunes and App Store on iOS are native wrappers around a WebKit UI, after all.)
So, while such theories are dramatic and link baity, like with the just-improved AirPlay and still not-fixed AirPrint, sometimes Apple can only implement so much of a new feature in the first release cycle. Therefore, it's probably safer to assume it's a bug unless and until it remains unfixed in a subsequent update. At which point even TiPb will start sharpening the pitchforks and lighting up the torches, b'okay?