Unfortunately, there's no detail yet on why -- we've heard that there may be local restrictions on VoIP technology that would block these kinds of communications. And this is only confirmation for the UAE, though it's probably a pretty good guess that other outages are legit as well. Stay tuned -- we'll keep an eye out for official confirmation in other areas, as well as a reason why this decision was made.
Update: The Next Web Middle East has a confusing writeup that suggests Apple pulled FaceTime because it was assumed assumed the feature would run afoul of the region's regulations around VoIP. The suggestion is that Apple made this move unilaterally, without consulting the carriers.
Update 2: We have a report from a Saudi Arabian source that FaceTime is working in the kingdom. However, subsequent reports show that once the iPhones are updated from the shipping iOS version, 4.02, to the current 4.1 version, the FaceTime feature drops away.