i dropped the illusion of recharging every two or even more days a long time ago.
Todays "smart" phones - at least mine :) - are constantly busy. (with near the power of desktop systems)
Checking emails, social networking, cloud syncing, news and weather updates, bla, bla, bla..
And on top of that, i do phone calls sometimes :)
I agree, that usage is the bigger factor - but i clearly see differences btw. different roms.
And the kernel - for example HP - can be very helpful saving energy with a little uv.