Hello
It's definately a feature and is controlled by the carrier. Orange UK's official line was this when i spoke to them
'The iPad does support HotSpots however we dont have plans to enable the feature now or int he future.' They do however accept feature requests so if you feel passionately you can speak to you network and tell them why its great.
It's also directly refferenced on this Apple support page : http://support.apple.com/kb/HT4517
It exists.
Tim
PS clearly only a feature on Cellular devices. WIFI only devices would gain no extra advantage of having it and when it's enabled, your usual wifi connection if you have it on cuts off.