Warlocks = strikers = mobility is important for their class. All of the striker classes have some means of mobility. Warlock's, being the magical/arcane striker [as opposed to the now 3 different flavors of martial-esque strikers] has teleportation instead of shifting. Their teleportation however, is USUALLY limited to a few squares. Outside of a couple of instances, it's going to be the equivalent of a shift, while sometimes they couldn't normally get their on a shift.
However multiple SHORT teleports [many you have to decide to use as soon as you get a chance and thus can't be set up with amazing effectiveness] are not as powerful as a single long range one. A 10 square teleport can get you to places it would be nearly impossible to get to otherwise. Even if you could have 2 encounter powers back to back with say 5 squares of teleportation, you can't teleport 5 squares into the air [or 5 squares across an open area] and then teleport the second time so that you end up on solid ground.
Also, wizards are not strikers, mobility isn't the main purpose of a controller, especially one that might be burning his move actions to keep spell effects going and moving them around the battlefield. Having the option of, when the pressure is on, hopping 10 squares away, possibly putting many of your allies, not to mention your sustained magical effects between you and the people coming to get you is huge. Sure, assuming no other conditions, 10 squares is easily a move and charge away for most monsters ... but wizards aren't likely to be in a generic space with no distinguishing features, no allies, no spells going, no conditions placed on the monsters that would make rushing the wizard more difficult, etc, etc, etc.
Considering the entire party needs to move to the location of the next encounter, the ammount of squares the warlock teleported during the fight doesn't really matter that fight. Unless he curses everyone he passes and waits for the party to catch up and kill those people, he's not really getting anywhere with all those teleports. [Compared to the teleportation powers available through rituals or 3E wizards, which can send you MUCH farther, and don't involve a string of walking distance teleports that require something to die adding up to a lot of area travelled without getting you anywhere, except a few times where you'll get across [or out of, or into] a pit or onto a ledge or some other strategic terrain within the encounter area.
EDIT:
Rogue's Great Leap Utility -> You get an AT-WILL, move action that lets you go as far as you want. So, with training you have 5, let's go with a brutal rogue type, so say, +3 for strength [at 1st], and you have the level adjust. At level 2, that's +9 to athletics, meaning you are hitting 10 minimum, 29 maximum, that's 2 to 5 movement at that point.
Fast forward to say level 8. You have +4 for level adjustment, your strength is now giving you +4 as well, with the 5 from training, that's +13, which can become +16 with a single feat. Now you are able to go a minimum of 3 squares, a maximum of 7 squares. Now jumping isn't as good as teleportation, but you can do this over and over again without rest or need to worry about meeting specific conditions. You may have to worry about attacks from people next to you as you leave the square, and you don't get the "line of sight but not line of effect" clause of teleports, but the at-will nature is huge. And, there is always a chance you might want to jump somewhere that you have line of effect but NOT line of sight to.
