So yea, the more they extend the moddability of the game (is that a word?) the more attractive they make the game, so even if they totally screw it, people might (and probably will) still buy it
People are still playing Oblivion too. Also, there are modders constantly making mods for Oblivion, so what is this lesson to be learned exclusively from Morrowind? Both games can easily be modded and Bethesda seems to understand their fans want to mod their games. Fallout 3 can also be easily modded. Modding is a good thing, but modding resources shouldn't affect the actual game. The console versions can't be modded. The game needs to be good, unmodded.