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...