The reason blacksmithing is more profitable is that if you tank you HAVE to have the gear. You can be a mage and still do well enough without top gear but the Tank just HAS to have the best he can get.

Mining/Herb is not the best in my opinion because there will not be a shortage of such items in general, if the price goes up then gold farmers will flock to that item and get a lot of them. Gold farmers do mine/herb, no reason for me to do so.