If your going to make that argument then we should get rid of Ability Power since it effects every skill in the game differently. It is completely ambiguous how much 100 ability power increases your DPS unless you memorize the individual ratios on all of your characters abilities, and that's not even getting into the fact that there are quite a few characters whose abilities don't become more powerful when you get ability power. That is a much larger burden of knowledge on new players than ability haste will be.

Honestly though this argument has a kind of a 'think of the children' feel. I expect new players won't have any more difficulty adjusting to ability haste than any of the other mechanics in the game, if anyone is going to struggle it is going to be players who have been using CDR for a decade.