I know of at least one stealth startup who have built up a javascript library that is indistinguishably performant with native apps, but that performance comes at the cost of progressive enhancement. It's a tradeoff worth making.
I believe in an open web too, but one that is as powerful as native apps, not a crippled second-rate one that loses users and developers to proprietary platforms. Any browser feature that developers find useful and actively adopt will quickly be incorporated into the remaining browsers.