Yeah I meant to point out points 1 and 3 as possible causes that influence point 2, training speed of passing. As far as I believe is been proven is that the elastic effect only works between a couple of skills, and there hasn't been shown a correlation between big men skills and passing for the elastic effect. Handling has proven to have an elastic effect on Passing, and I can imagine that there are plenty of bigs with low initial passing and higher handling (because of starting skills or 1v1 training that can be done for PF's). Those bigs will benefit from the elastic effect, and thus will train faster in passing.
The elastic effect works both way in regards to speeding up or slowing down, so if a player has 7 Passing and 1 Handling, his passing will train slower because it's kept down by low handling.
The elastic effect doesn't work both ways in regards to passing having an effect on training handling, at least it's not proven yet. Rhyminsimon created the Training Simulator
(229484.1), and in the last worksheet of the Simulator he put the elastic effect and which skills affect what skills and in what way. There you can check out the known correlations of the elastic effect.