@j0lter: I think it's better this way. If you're making a bunch of different teams to play online it'd be frustrating to only be able to use a TM on one single pokemon out of 500+. Lots of the TMs were one time only and couldn't be bought, this way gives better flexibility.
This so much the one time use with tm's was very annoying when making a competitive team.
I wish the HM's where more useful, the only HM that's good is surf the rest are just garbage.Maybe if there base power where higher and had a good secondary effect I would use them more.