They are, but under the current model the broadcasters don't know which ones would be the dead rubbers until the season's about half way through, so they've got to buy the lot, warts and all.
Under the tiered system they'll know in advance which 50% of the games are dead rubbers and the TV deals will be weighted appropriately. Not to mention that some of the biggest drawing games, like Essendon vs Collingwood for example, would disappear out of existence some years. No showdowns some years? The people of Adelaide wouldn't have a reason to get out of bed.
I see the tier system as being the ideal way to greatly diminish AFL revenue and obliterate interest in the game for supporters of half the sides.