|Kitty is thinking with portals.|
Use 1: Class Trainers - Yes, when leveling up, you should visit your trainer every few levels. But look at what they are changing in Cataclysm. You will get a talent point one level alternating with skills every other levels. So really, at the most frequent, you should go over 2 levels. If you are leveling fresh from 85, this means you would go a grand total of 42 times to get skills. Take into account that druids and death knights have ways to get to their trainers in Ebon Hold or Moonglade without going to the city, and it becomes even less. In addition, you don't get enough skills to warrant visiting every 2 levels. You could probably go once every 10 levels and be okay when leveling. This cuts the times down to 8. Not a really good reason to have a hearthstone in a city. And after level 85, then what. You never go back to your class trainer unless you respec.
Use 2: Profession Trainers - Most people power level their professions anyway and just buy the mats and use professions that make sense with each other. You can go to a city once and level a profession up to 525, which is what I'm guessing the next profession cap is going to be. In addition, things that take multiple mats level you up faster.
Use 3: Hubs - Just because there is no central city in Cataclysm doesn't mean there won't be a hub. You have the PvP Wintergrasp like zone that will likely be a HUB. In addition, each city is bigger than any of the central cities before. It will cut down on lag if everybody in your faction is in one to two cities. I have a super powerful system and I still only get 30 FPS in Dalaran.
Use 4: Battleground Masters - Since you can queue for battlegrounds from anywhere in the world, this is pretty much a non-issue.
Use 5: Guild Bank - Taken care of in guild rewards. Start a raid, summon the bank, get your flask, etc. Keep going.
Use 6: Flight Hub - With the addition of buying 310% speed for 5k in Cataclysm, your mount has become faster than the flight paths (and more direct too, but that is another issue entirely.) You can fly there faster yourself than you can with a flight path.
Use 7: Switching Continents - It is true, this is probably a reason you will come back to your central city because they are the ways you travel to the other zones. Unless you can find a mage, this is probably unavoidable. I wouldn't be surprised to see them come out with new mage portals. Plus, they could just do what they did with getting to the Dark Portal and just add a portal to say Dalaran in each city or portals to the other continent. And not all of those paths are through cities. (Hello Wetlands, we have not forgotten about you.)
Use 8: Auction House - Ah, the most brilliant part of the plan by Blizzard. Auction House is the one legitimate reason to go to the cities still. Unless you have the remote AH, you have to go to the city. But taking away the portals makes it harder to go to the city. You are in the middle of Hyjal at level 82. Your bags are full with stuff you want to sell. What would be easier? Go to the city. Or just go to the local home, get resting XP built up, sign off for the night, and then just do your AH stuff away from the game. You come home, your bags are empty, and you are ready to keep going on questing. In other words, Blizzard incentives you to start using the remote AH by taking away portals.
So as you can see, cities are not as important in WoW as they are now. And they will become less important with the addition of flying. The only reason I left out was Trade Chat, and honestly, who wants to spend any amount of time in there. So there is no reason to freak out yet. Especially considering we are probably still about 2 months away from Cataclysm, this could be changed back still. I'm not counting on it, but it may happen.