While it may be your opinion on why DII teams historically haven't "played up," it is a bit of an unfair statement, considering that only very recently the criterion for DII playoff selection changed to no longer penalize teams for playing outside their division. If playing up kept a team out of the playoffs, of course you wouldn't see it happen a lot, regardless of the size of the fish and pond. Of course, the big fish of the ponds are also the teams that are most likely to have a shot at the postseason and least likely to take any scheduling steps to jeopardize that.
My 2 cents on that. Carry on with your debate.