Compatibility of course. Instead of recoding 100% of an app to run across multiple platforms, code an HTML5 layer for consistent look and feel for all and address unique aspects with lower-level code. So that the average app could be, say, 50% common code and 50% native. That saves time for companies like Rovio who like to land on every platform.

In addition, not every app needs the native horsepower or functionality. HTML5 will be able to address a great many handy little utilities by itself.

I can understand why C++ developers get overwrought about paradigm shifts like this one, but really, there is nothing to fear, belittle or berate. Just another tech evolution.