The difference is whether you have the ability to fly between turns. A creature with a flight speed does. And since the default flight speed rules assume wings, it makes sense to have rules for momentum- move at least 2 spaces, or you crash. Alright.0You seem to be presuming that flying and having a flight speed are two different things, but I'm not aware of any rule that makes such a distinction. Are you aware of such a rule? If so, please point it out to me.
Until then, the ruling by customer service seems perfectly reasonable to me.
Meanwhile a creature without a flight speed who was granted the ability to fly by a power has the ability to fly as long as the power grants it. In this case, for one move action during which you can fly a maximum of a particular distance. A normal reading of the power would suggest that you have the ability to fly while its active, and then not while its not. It does not make sense to take rules designed to mimic momentum and then boot strap them into a full round of hovering after a power's defined effect has ended.
The upshot of this ruling is that all non-fly-speed-flight now has an "until the end of your next turn you can hover if you moved at least 2" effect built into it, unless it specificaly states otherwise.
Which is kind of awkward at times. See above for details, the amazing flying rhino, etc.