An objection I've heard raised here -- actually, two different objections, but with the same root -- is (1) people don't want to open their web browser and surf to a web page to run their programs, and (2) the mobile web browsing experience is not terribly convenient.
What's critical to realize is that "web apps" aren't necessarily bound to the experience of "opening up a web browser as an explicit action, navigating to an application's web site, and then interacting with it as if it were a web page." Web-apps-as-first-class-apps is a viable model for development and deployment. And there is a team of people inside Mozilla who are working really hard to make this work as seamlessly as possible.
I recognize that neither platform has the penetration to be a real game changer; at least, not at the moment. I'm holding them up as existence proofs that the approach of "web app as native app" is viable. But let's talk about how these technologies can be leveraged for native webapp deployment on Android, iOS, and Desktop systems.
This is where the work that Mozilla has been doing for web app deployment comes into play, and it's easier to demonstrate than it is to explain. If you have Firefox installed on your desktop (or Firefox Aurora on your Android device), you can go to https://marketplace.firefox.com/, find apps that amuse you, and click on "install." At that point, Firefox takes the steps necessary to put an icon in whatever location you're used to finding your applications. On your Android device, you get an application icon. Under OS X, you get a new application in Launchpad. For Windows, you get... well, whatever your version of Windows uses to access installed apps.
From that point forward, the distinction between these web apps and native applications is impossible for users to discern.