All of those and also, a 4th that is a parallel to 3--added complexity and preponderence of rules leading to unintentional exploit combinations.
This is exponentially more problematic with 3rd party stuff, as WotC (until some of their insane recent books that seem in light of 4e to be intentionally unbalancing to see what happened) generally tries at least a little to avoid these, but they don't read 3rd party stuff, so they can't try to avoid overpowering combos.
It's just a different paradigm here for proposals--we're trying to be careful about balance while allowing a good amount of official material here, but we tend to look askance at totally homebrewed or 3rd party material. On the other hand, Living ENWorld only uses open content and has accepted some free 3rd party material in the past (I think it was from the netbook of feats).