I was thinking the same thing, extend taxi to burn the extra weight. Personally, and I'll say again I haven't flown jets, this may have been the best option.
My understanding as I'm currently working on ATPL performance, is that a 727 has 150kg allocated to be burnt by the time it reaches it's BRW, In this is the case than surely a full plane of happy pax is the best way to go?
Unfortunatly the world we live in is full of threating litigation and media that can have a story to millions in just minutes. I think the pilots did the correct thing legally but may have avoided the media attention by just burning the extra fuel in taxi.
Just my two cents,
Rocket