Well I think that incremental delivery of applications, crawlability, URL bookmarkability and being able to push live updates are valuable features the Web has already solved. In general iteration speed in dev is better too (usually lower compilation times)
Don't forget the cost of managing multiple platforms and not having to have multiple dev teams. On the teams I've worked with that has been the reason for going with html5 apps.
How many businesses want to build the same product 3 times (at least) for different customers and will they be able to get it all implemented at the same time, or try to manage the differences when they are all communicating with the same backend service?
It's just a non-starter for most start-ups or non-technology focused businesses.
