They do a live stream as it's more FUN, they'll edit it all to make it look better later - they always do. No two ways about it though since Mike Morlan left the audio issues have become more of an issue and they don't seem to be able to get a handle on it.
It's no where near as simple as many people think to do a live stream the way they do it - multiple sites, multiple cameras, multiple mics on multiple continents. Personally I'd rather they moved to a split - pre-record the marketing guff, the Q&A and then have streams of the competitions (which I REALLY enjoyed). This is how WMH use to do it, Mike would pre-record/edit sections they could throw in whilst they setup the next interview etc.