The concern about power management is relative and needs to be put also in its context. Even if in principle a well written native application will be more power efficient than a web runtime application, in practice the user might get no negative impact if the application is useful for simple actions.

For instance, I miss an application telling me where to go to take the quickest public transport to reach my home, based on my location and know timetables.

Imagine a developer goes ahead with a Web Runtime app because it's actually easy to program. I don't need to have a permanent widget polling data to tell me the nearest / fastest ways to reach my home. It happens perhaps once a week that I'm in such situations and I would just need one minute of use time of such app for being useful.

I also see the Web Runtime as a good development path for mobile developers. It's a good entry point for regular web developers giving a try to some basic ideas e.g. optimized clients of web services. Once they start in mobile development they get into more complex ideas, perhaps they hit some limitations in terms of APIs or performance and they start being interesed and learning in more native-ish programming. Qt offers an interesting transition path between pure Web Runtime and pure native Qt.