I believe that to be a fallacy in this context as HTML5 will solve none of the fundamental problems. For example iPhone people often say HTML5 but they mean 'iPad/iPhone version'. While it will make a few things easier, the basic problem, the client-independent content distribution remains the same, you would still have to have a 'desktop HTML5 site', an 'iPhone HTML5 site', a 'MeeGo HTML5 site', etc.