It's unlikely to be battery concerns. If anything, lack of extensions and low limits means webgl code would have to perform multiple passes of a scene to achiev

It's unlikely to be battery concerns. If anything, lack of extensions and low limits means webgl code would have to perform multiple passes of a scene to achieve the same visual effects, thereby increasing the battery drain. Also, why allow these features for native apps if it's not good for the battery? And if you click through to the webkit bugtracker, it looks like almost all the issues listed already have patches committed.