The mechanics of the plot are more important here than the justification. Of course Jake's action makes sense
(due kudos to Cameron, honestly); but it is also a useful way to put the new kid on the top of the food chain.
As far as symbolism goes, I did like the film's suggest that the contrast between the two bodies was that of a sleeper dreaming. It's also a story about a sleeper identifying with his dream and evaporating into it, as surely as a chubby guy and his WoW avatar (...okay, me).
It's not insignificant that one of the first comments in the film is Jake noting the absence
of dreaming while in space.