using the 'quick mode' focussing when on live view flips the mirror down, uses the faster normal af, then flips the mirror back up.
using the 'live mode' focussing is slow, because it reads all its information from the sensor and uses some sort of contrasty-algorithm.
but yeah, every other camera, P&S and EVIL like the NEX, they all read the contrast information from the sensor too, and they're faster than the 'live mode' in the dslr.
so just based on that, i'd say it was the algorithm. but canon and nikon also produce P&S cameras, which can only read information from the sensor. Does anyone have a Powershot handy? Has anyone compared the speed of focussing a powershot/ixus/whatever compared to a dslr on live-mode?
and there's also other factors, the size of the sensor, pixel density, and don't forget the size of the lenses, the travel distance from full macro to infinity focus.
(there's a thing that bugs me, if i use live mode, most of the time when it tries to focus it pulls the focus all the way from one extreme to the other to try get focus, the algorithm obviously doesn't realise it's going 'the wrong way' until it hits the end. obviously the algorithm could be improved in this respect).