The whole breakable TM's thing was a bit of a burden (albeit a necessary one since the games didn't have nearly as much storage space as they do today) in Generation I. Previously, I used to hold onto TM's because I felt like I didn't want to use them immediately or I may find a better use for them. But in Generation I, it was that much more annoying when you stockpile so many TM's and HM's because you're scared to use them and then your PC becomes too full to carry any more and your bag becomes too full to carry anything else, so you end up wasting the TM's you don't picture yourself ever using just so you can use your bag and PC storage again!
Now that they're unbreakable, I don't have to feel forced to use them, and the game isn't any more or less difficult as a result. Also, now that we don't have the PC storage system I don't have to worry about them filling up my box or my bag, solely at the cost of the laws of physics no longer applying to the game. So in short, yes, unbreakable TM's is definitely a great innovation. I'll admit I was a tad skeptical when news broke that TM's would be unbreakable in Black/White (What?! A change in formula?! I'm going to narrow-mindedly write this off as GameFreak losing their minds and destroying what were once sacred traditions between generations!) but as I played, I began to find it more and more helpful. I mean, in general, I have a tendency to only use a TM once anyway, but the fact that I know I'll still have it later really relieves me of any pressure or apprehension I may have about using them.