The great thing, and also the terrible thing, about web apps is that they're universal. Make an app somewhere and anybody with a computer can get at it, usually without paying very much. It's a great opportunity for people to make things. It's also a shame, because most web apps encourage people to spend more time in front of a computer (instead of helping them take care of business more quickly than they would otherwise, so they can close the computer and get back to everything else), and because as wonderful as computers are, they're limited in their impact on the physical world.
Further complicating the matter are advertisers, who are still desperately seeking the next frontier once print and television ads die. Advertisers like web apps, because web apps have lots of users, and that means lots of potential targets. Robots? Not much advertising potential.