Saying HTML5 won't be 'production ready' for a while, and saying that HTML5 will never be production ready are two very different things, but I feel people conflate the arguments all the time.
If you do believe that HTML5 will eventually be production ready, even if not for another 2 years, ask yourself this: when that time comes, do you want to be the guy with 2 years experience or the guy with none? When the industry is ready, 'HTML5 developers' are going to be all anybody wants and they'll want them all right now. If you want to jump on a moving train carriage then you have to start running towards it very early...
I am guy with more than 10 years experience, I am on WHATWG list since prehistoric times, when HTML5 was still called "Web Applications 1.0" and I will gladly use it for web content, but for mobile applications I choose native.
When the time comes? Do you think that this would be a well defined time? Will someone declare it 'Production Ready' one day? It is going to be a very slow transition (painfully slow). Once most thing are transitioned, other technologies will be so far ahead that 'web applications' will no longer exists. Content web sites will always exist, but not applications.
If you do believe that HTML5 will eventually be production ready, even if not for another 2 years, ask yourself this: when that time comes, do you want to be the guy with 2 years experience or the guy with none? When the industry is ready, 'HTML5 developers' are going to be all anybody wants and they'll want them all right now. If you want to jump on a moving train carriage then you have to start running towards it very early...