WMM is free, and some pretty neat stuff can be done with it for free. Add-ons which can add a whole new range of features for a minimal price can make it a worthy competitor of the top editing software out there.
I'm not saying it's the best out there - Vegas likely is still the front runner. But considering that's hundreds of pounds to buy (or dollars, whatever) - WMM can provide a skilled editor with something that can likely mimic any edited stunt video seen here on GTAS, based purely on editing alone, and not leave them with a big hole in their pocket where their hard-earned cash used to be!