RAM available in mobile phones seems to grow exponentially [1]. Power efficency of processors also seems to grow exponentially [2] (does anybody have a source for ARM processors?).
Power usage has little to do with memory usage. In fact, if the browser is using more RAM as a cache, it won't hit persistent storage as much, which actually increases battery life.
If that exaggerated RAM use causes other more intensive apps and their data to be evicted, that can cause a much more significant load when the app has to spin up again and re-acquire or re-calculate its state.
The extra chips are not free. What we are seeing is bringing up the latest low power tech into the phones for now. Except RAM has hit maximum densities per chip already or is very close.
Remember that RAM has to be powered on for every refresh cycle...
It is "nothing" compared to screen or radios, but it is there. So you won't be seeing more than one Dram chip in there, footprint notwithstanding.
Browser are caching web content, not much persistent storage content... and the OS does persistent storage caching fine, typically no need to try to add your own (poor) layer to do that.
