Logically:
Separation - Have to be fast enough to outrun your defender(speed), quick enough to accelerate before/beyond your defender (speed/agility), smart enough as a WR to know your route and run it without hesitation off the line (no GLB association, probably automatic?)
Depending on coverage, just like in normal football, certain routes will get you separation without any athletic ability aside from knowing your route and executing it correctly.
Catching - Knowing where the ball will be going in your route (catching), seeing it coming - most importantly during the last couple seconds (vision), turning toward the ball with appropriate timing(agility, perhaps catching, perhaps vision), the know-how of catching - putting it into your hands and not against your body - something typically learned through the experience of catching the ball over and over(catching), and finally the ability to continue your stride after the catch instead of standing there like a sore thumb (catching, agility).
Perfect passes are obviously easier to catch. High passes will have to be accounted for by jumping athleticism, which would take into account catching, vision, jumping, and probably agility as well.
YAC - Most receivers, commentators, and general critics of the sport do not consider YAC stats to be nearly as important as simply catching the ball and making the initial pass yards. However, in order to achieve high YAC a number of options are available: Juking your back's ankles out from beneath him - my favorite (agility, speed, carrying, vision), powering your way through -likely more difficult for a WR to focus on considering their emphasis on elusiveness and speed (strength, carrying, agility), or finding that sweet spot to just catch the ball and run it in - usually related to the level of competition (vision, catching, speed, agility)
In my opinion, running style has a lot more to do with powering through for WRs. CBs don't have a tremendous amount of strength, nor do wide receivers; what makes the CBs tackle effective isn't their strength though, it's the velocity at which they tackle, their ability to wrap up your limbs, and the angle they know to come at you. Vision may have a part in seeing and avoiding these things, maybe agility.
Sorry if that was long-winded, but
Agree/disagree?
Edit: Obviously WRs can perform well without being mindful of any sort of natural logic considering this is a game of checks and balances, for the player, his competition, and teammates. What I'm trying to point out is the possible logic behind the programming/vision/direction of the game. If you disagree just say so, I won't be offended. :-p
