This thread is a deceivingly good discussion. When I happened on to it, I was rather indifferent to the poll question but wanted to see where the consensus of the FIRST community stood. Admittedly, while reading the through it, I have been swayed toward legal and,to illegal, and back again, and so on....
After taking in the thread thus far, I think that...
The swapping of the drill motor lends itself to swapping of other common parts between the modular components: Jumpy and Grabby. With this line of reasoning, all the bolts (inherently heavy), for example, could be exchanged from Jumpy to Grabby and back again. For inspection Jumpy could be on the robot, and Grabby would be just a pile of aluminum waiting to be assembled. This even goes so far as give the team the benefit of the doubt that no "spares" were used and that parts were actually swapped out each time. I think common sense tells us that this example is a bit far down on a slippery slope of what is technically considered legal. (i.e. it doesn't pass the "spirit of the rules" test, particularly the pile of aluminum being a mechanism)
The rules have got to be more than just unverifiable proclamations of legal verses illegal. There must be a way to clearly define what is legal and what is not; an ability to check that the rules are being followed (not to give up on gracious professionalism, but as a way to spot check and ensure the integrity of the game.
I think the heart of this is not about swapping parts between the modular components, but rather if modular components need to be
complete (ALL pieces/parts present to function) to pass inspection (for 2004).
With this focus, it gets the scenario away from the uncheckable grey area of whether or not they actually swap the motor between the two components, and back into a hands of the inspectors where a consistent ruling can be made and rules can clearly interpreted by all teams.
..and isn't consistency in the rules all we really want each year

...consistency from kickoff to the ship date...consistency from match to match, competition to competition...
-Bill