Several people commented on the inconsistency in whether they do a tribal/eviction or not after someone is pulled out of the game. My bet is that the decision depends on a number of factors. Examples include:
1) Was the person pulled before or after the immunity challenge?
2) If pulled after immunity challenge was the person on the same or different team from the one going to tribal?
3) If before immunity challenge but challenge has already been constructed will that challenge work with x-2 contestants or x-1 contestants then originally planned?
4) How does getting rid of one vs. two people play into the entire scheme of things (i.e. numbers for future challenges, when merge happens, etc.)?
I bet they look at several things before deciding which scenarios to use.