I keep hearing this. Could you explain why pure web technologies with no other options is better than giving developers the best of both worlds (deeply integrated web apps as well as native apps, if the performance is needed)? HTML5 browser technology isn't even able to render current iOS games in full blown desktop browsers, how is it going to be adequate for embedded devices in the coming few years?

In the long run you may be right, but it's going to take quite a bit longer and until then the mobile market is going to be even more entrenched than now.