The alternative would be maintaining many toolkit backends. We already see how well that worked out. Qt backend wasn't maintained in a while, and fell into bit rot. That basically prevents Firefox from being used Plasma Mobile and the like. Having HTML backend is better than having none at all.

> I have to say though, having chrome that is virtually indistinguishable from a webpage is a phisher's dream.

That's not terribly hard to do today either. That's why browsers implemented those obnoxious fullscreen animations and notifications somewhen last year.