MobileSafari has fantastic HTML5 support. Unfortunately, a few important features are buggy or crippled; offline cache is very hard to work with (as detailed in markbao's length comment above), and WebSQL tops out at 50 MB (with very UX-unfriendly alerts at every 5MB of new storage).

I don't think this is intentional malice, merely simple neglect from Apple. Unfortunately, the result is the same. :(