Agreed. I would like a caveat such as "Lasts till end of next round, Sustain : Power is sustained as long as the fighter scores at least one hit with a basic melee attack or fighter power" so there is at least SOME way for creatures to break it other than teleports.Yeah, and there's no excuse for making a power that immobilizes indefinitely without a save.
My personal guideline in these disputes is to ask the player to describe why the power would work the way he thinks, speaking in-game instead of by rules references. If he can't, then I go ahead and rule the way I was going to. So I would have asked, "the dragon is pinned even though you can't move? What are you doing that pins it?" And if he gave me something plausible, I'd go with it. If not, I'd say that he had pinned the dragon by fighting with it and that he can't now that he's unable to act.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.