Speed vs. Priority

a) are there other significant factors that determine the priority of an attack across the board, aside from its frames of execution?

You basically have to think about how an actual hit is registered. Obviously it's not all based purely on stats. The first thing that comes to mind is that some sort of collision must occur, and hence distance becomes a factor. The second thing is I believe that with each attack there are areas, or in the case of 3D, defined spaces designated as "hit" or "vulnerable". If your hit space comes in contact with your opponents vulnerable space, then you score the hit. While I have no hard evidence to support this, I think it's fairly commonly used across most fighting games (2D and 3D). So when two attacks are thrown out, not only must the frame stats be considered, I think you have to take into account the type of attack being made, what hit space it has, what vulnerable space it opens up, and then it becomes a question of who hits the other guy's vulnerable space first.

b) is "priority" just an illusion caused by the fast recovery from previous moves? ie, if a character recovers faster than he appears, his next move will come out a few frames sooner than his opponent expects.

With the above, I look at "priority" as a measure of the hit and vulnerable spaces of an attack. An attack with a large vulnerable space is obviously going to be easier to hit out of compared to an attack with a small space, and hence would have a lower "priority".

__
m y k e
how ya gonna win when ya ain't right within?