I agree about the initial risks - they are probably equivilant for a startup making a webapp versus a startup making a game - what I'm saying is that the position you find yourself in as a game developer after getting traction for your first product is much worse.

With a webapp you can build a company around that traction and potentially get acquired without developing another product. With a game studio, you then have to make the next game, and past success isn't nearly a guarantee of future performance. You can do sequels, but even this isn't bullet proof.

As other commenters pointed out, there are exceptions within the marketplace. And if you're doing a gaming startup that's where you want to be.