My main profession is Leather-working, which has its ups and downs. I initially took it up in the hopes of providing armor for myself, but I found that that was pretty much not happening in Classic or BC. We shall see if Wrath corrects this or not.
One thing that Leather-working had in Classic that nothing else had was the means to upgrade lower level leather to a higher level, such as Light Leather -> Medium Leather -> Heavy -> Thick -> Rugged. But with the advent of BC and Wrath, this has not carried forward. Rugged cannot be upconverted to Knothide, and Heavy Knothide cannot be upconverted to Borean. Yes, you have Borean -> Heavy Borean, but that's it.
What annoys me about this is that this further disconnects Classic from the rest of the game. All the leather you gathered in Classic was rendered immediately irrelevant as soon as BC came out, and I imagine that nobody ever hunts Clefthoofs anymore other than for quest-based advances.
Another profession that likely has similar issues is Engineering. As annoying as it might be, Classic Engineering uses components from the start throughout its levels - copper for copper screws, for example. Yet, once you hit BC, I am willing to bet that that gets thrown aside (I haven't confirmed) . While I can imagine many an engineer gleefully dumping that last stack of copper bars (... or cursing that he didn't keep it in ore form for the new Jewelers) to make room for Fel Iron bolts, I can't help but notice the solid barrier of irrelevancy between Classic and BC. And while I haven't researched this, I bet that there is a similar barrier between BC and Wrath.
What this does, for those professions that have continuity, is turn them into three different professions, sequential to each other. Once I hit BC, all that Dragonscale training seems pretty worthless, for an example.
It puzzles me that Blizz has put so much thought into making the three different games ( ... and they do play as three different games) so alien to each other, instead of integrating more continuity and involvement between them. It seems to me that it would make it easier to balance the carrot and stick approach to keeping people playing, for example.
It's so bad that you can't even go to a Grand Master trainer in Dalaran and learn something that a Master, Artisan, or earlier, could train you. Enchanters especially love this since they have to fly out to Hellfire to train until they hit GM status.
I do not understand why a company would invest so much time and money into something and then just cut it loose like that (But that's another post.) .
One last thing. Engineers have planes and choppers. Now Tailors have flying carpets. I've been thinking on it for a while and have finally determined what the Leather-worker's mount analog should be (Especially now that riding crops are nerfed to the ground) . 1,000 League Boots. All the advantages of a mount, without actually being astride a mount. What's not to like?