Skillups for trade skills are based on levels now. And gaining xp in a tradeskill level is only based on two things. The combine and your current level.
Your current level determines the difficulty of the combine to a certain degree. Thus, much like the exp difference in killing a white con versus a green con, performing a white con combine will get you more tradeskill xp than a green con combine (assuming you were as successful with the white con as you were with the green con).
The amount of xp you get also depends on how high the quality of the result is. There are at most 4 levels of quality you can achieve. I've found that each level is pretty close to a multiplier of xp. ie level 3 quality gets 3 times as much xp as level 1 quality (it's actually a bit different than this but still a good approximation). Also, you get more xp from final result combines than interim combines. ie the combine to make a chainmail tunic gives more xp than the combine to make the chain rings you needed to eventually make the tunic.
I know this from a combination of beta exp and a post that was made where the devs stated that they didn't want stats involved because it would favor adventurers and certain race/class combos. All races will be equally capable tradeskillers without including the racial traditions (which are supposed to be very small modifiers anyways).