One thing to note with burst is that it works on crit immune creatures. It just requires confirming a crit, not actually delivering one. So even if the foe cannot be crit, you can still get your extra 2d10 damage or whatever (on top of the 1d6, another thing some people forget).
Just pointing that out, since most DMs seem to unfairly nerf the burst properties due to their rules understanding. Burst still sucks bucketloads of ass and I would have done the same thing as you.
