I would venture to say that the relentless push to move as much as possible to the client has much more impact on battery life than the handful of ads we typically see.
Every measurement (not many) I've seen suggest that screen (size/resolution) and network are the main culprits, outside of very intense CPU/GPU client (e.g. games). I don't think I've seen a really good analysis, though, so would be interested if you've got a reference.
number one killer of my battery with last 2 phones? Wifi enabled. Doesn't matter that much if actually used. Turn it off completely, phone lasts 2-3x more.
No matter how many cores are in your phone, web browsing will always be able to use only a single thread. JS is inherently multi-threaded, the only thing that could use multiple threads is the IndexedDB bullcrap (which ain't properly supported by iOS anyway), and background loading of async resources (which is network constrained on mobile, so MT doesn't help).
This is totally untrue. Layout can run off the main thread if engineered properly. Painting and compositing already do in some browsers. Layout, painting, and compositing are inherently parallel problems, so any one of these tasks can saturate all your cores if done carefully. Iframe JS can run in multiple threads if engineered right.
