I didn't really know where to put this, so I put it here :p
Anyway, here's my suggestion!
Instead of releasing individual episodes (like Wallace & Gromit) and potentially lose out on sales, and instead of selling full "seasons" (like Sam & Max) why not try this idea....
Release a free portal "game" that basically acts as a menu, and release the "episodes" as addon content, with an appropriate price :)
That way you have the advantages of releasing individual episodes (extra achievements for the GS mad, lesser file size limits, etc) AND the advantages of full seasons (a guaranteed (well, not quite) sale for every copy sold, rather than hoping each episode will sell as well as the last, an easy way to access bonus features, etc)
More importantly, it would allow the TTG preorder model to work on the 360 with no problems at all! You could put the portal "game" online a month in advance, for say, 3200 MS points, and every month release a new "free" addon, with chapters of the game!!
Simular ideas can be seen in XBLA game "Family Game Night" - I think this idea would work really well for TTG. Anyone's thoughts?