Technical Incompetence

"I'm pretty sure my choice of Water Pokemon is about to get future endeavoured. It failed Test 1: 'Can it use TM13?'"
- Twitter comment in reference to Gamengorge, 9/28/10

In my many Black and White playthroughs, this isn't the first time I've been shocked - SHOCKED - that a Pokemon didn't have the capabilities to use a TM. It seemed to be endemic to the Water type as I learned when Swana was compatible with Ice Beam, but not Blizzard, but upon further digging over at Veekun it seems that certain rules from the last generations are being chucked out the window.

Specifically, the rules would be:
- Starters get wide compatibility for attacking moves, and the final forms get Earthquake. Not this time: Snivy's compatibility is Grass moves, Aerial Ace, and Normal moves, and neither it nor Oshawott's final form (in correction of something I posted in the tier lists) learn Earthquake. At least Tepig's family did all right (but it also gets the benefits of two STABs).

- Water types learn Ice Beam and Blizzard, full stop. (Not anymore: Gamergorge doesn't get either one, and Swana misses on Blizzard as previously mentioned.)

- The average final-form Pokemon in gen IV had roughly 40 TMs (30 + mandatory 10) that they learned. With 3 more TMs and only about 20 existing ones changing, this has gone down to only 15-20 over and above the mandatory ones in gen V.

So what's responsible for the changes?

The biggest thing is probably the fact that TMs are now basically HMs that don't require the move deleter to get rid of. Once you get say, Ice Beam and can throw it on anything that moves, the game needs to restrict the Pokemon that have access to it. (Especially given that you've already beaten the Dragon gym).

Another factor is that some of the newer TMs pay much more attention to flavour than they would have in gen IV. If Ice Breath (TM79) existed last gen, it probably would have gone to every Water type not named Magikarp (giving it an automatic learnbase of 90+ Pokemon) and probably a few Dragons (like the Latis). Instead, its movepool is roughly 15 out of 649, and all of that is Ice types and Mew (who of course learns everything). There's no Pokemon (again, Mew excluded) that can learn Ice Beam and Boiling Water simultaneously, and there's an obvious reason - if you're capable of breathing Ice like that, you can't emit water hot enough to be "boiling".

Lastly, there's still the factors of last gen's TM base to consider. Remember, we're one generation removed from Stealth Rock being either one of the first two TMs you get (in Diamond/Pearl/Platinum) or buyable for $2k in a department store (HG/SS). They've gone to great lengths to reduce Stealth Rock use by seemingly preventing it from showing up in random Wi-Fi battles, and TM76 is now a 30 power Bug move (which makes it as unappealing as you can get). If Stealth Rock was introduced in gen V, it would likely have its natural movepool (which is all Rock-types) + maybe a few Ground types, and that's it.

So on March 6, make sure to keep a Pokedex handy online (such as Bulbapedia or Veekun) and check that TM's capability before you start throwing it around willy-nilly. You may not like the results.