From: Olympia, WA
If you REALLY want to spend the time and unbalance the game against the AI (because you will), you can open the AE Editor, pictured in a post above, at the beginning of the scenario, select the units you don't want to be restricted, and change their HQs to an unrestricted HQ. That way, when you start the scenario, they will not be restricted and you can move them freely. Problem with this, as others have pointed out, is the potential for unbalancing. But, it's your call.
It is a pain as the Allies in the beginning to have all these restricted units you can't move. But it gets better over time. The decision, I believe, was made to reflect some of the political realities of the time, so you cannot, for instance, move Dutch units to Midway, for example, or West Coast units to Burma, because no leader at the time would take the political risk.
Desert War 1940-1942 Beta Tester
Agressors: Ancient Rome Beta Tester
"The greatest and noblest pleasure which men can have in this world is to discover new truths; and the next is to shake off old prejudices." Frederick the Great