Well, noticed how Android's own web browser is even worse in HTML5 than Mobile Safari? And this is Google, the guys that really like mobile html5 apps.
Fact is, it's not that easy to make a good mobile browser --heck, it's not that easy to make a good desktop browser.
Still, desktop HTML5 leaves a lot to be desired. Forms support is lacking, the audio side is neglected, SVG still lacks features and is not properly accelerated (even the latest IE that just got it is better in this regard), the client side storage didn't pan out well, typography is still crappy, etc. And this is for the desktop, that doesn't have the battery, memory and performance concerns of the mobile.
And it holds true for Safari, Chrome AND Firefox.
So, in case you're thinking Apple is doing something especially malicious here, well, they are not.