Earthquake is one of the best moves in the game, don't be fooled. Ground is only resisted by Bug, Flying (immune), and Grass. It hits Electric, Fire, Poison, Rock, and Steel (the best defensive type) super effective. 100 BP and 100 accuracy makes it the most reliable and powerful move in the game with no drawbacks whatsoever. When you consider that all Pokemon who learn Earthquake have access to a move to hit Flying / Levitate Pokemon hard, along with the extremely large distribution, it isn't hard to see why it is the most used move in competitive battling.
The Infinite usage of TM's is a fantastic addition; any competitive battler will be ecstatic about it. It was a huge waste of time before, having to restart entire games just to get access to different TM's. Such a huge waste of time, in fact, that many players hacked for them. This addition should reduce the amount of hacking, but also provide greater variety in the online battling community. From the in-game perspective, it won't be broken, either. The games were never known for their difficulty, so if you wanted the game to be more difficult you had to set restrictions on your actions in the first place. Preventing the use of unlimited TM's during your play-through will accomplish just that, and for younger children it may make the game easier. This can only mean good things.