Even if you purchase training of a skill, that only gives you a rating of 1 in that skill. You still need to perform the skill a lot for it on increase, and in tradeskill's case, that means doing menial combines until you can do better stuff. True, you could buy all that in the AH, but it isn't like you can just buy yourself artisan level in two skills like *snap* that.
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Only the exceptions can be exceptional.