In the long run it will only benefit third parties to have Nintendo more successful then the competition.
Despite Nintendo having always been their own consoles number one software publisher their has always been alot of room for third parties to profit. On the GameCube Sega sold more copies of their titles then on any of the competitions far more successful consoles.
Basically your not looking at all third parties profits rather at just a few of the major ones. Atari reduced its yearly losses big time thanks to their DragonBallZ game being a major hit in European markets. You also saw an increase in UbiSoft's profits and Konami's and Sega saw a small increase too.
In the end the only third parties in bad positions are the dumb ones who didn't think the Wii could amount to anything. I mean the DS should have proved that Nintendo's innovative approach could yeild major profit margins. So when publishers like EAGames didn't jump on the bandwagon that was their own stupid fault.
Think about it according to NamcoBandai a big budget Wii game can be developed for around 4-million USD while a big budget PS3 game goes for about 30-million. So thats alot of extra profit the Wii game can make I mean 25-million more dollars then the PS3 one.
So why didn't more third parties use logic? thats the real question!