Guys, let me drop a truth bomb on you if you think that third party exclusives aren't important, and that just getting multi-plats is okay:
Looking at Wikipedia, the Gamecube only sold about 21.4 million consoles worldwide. It came in last place during that generation, not by a large margin compared to the Xbox, but not for a poor reason. Anybody who owned or owns a Gamecube can tell you: almost every title worth owning is a first party title. Almost every third party title is a multi-plat, and whatever exclusives there may have been weren't exceptionally notable when compared to what was appearing on the likes of the Xbox and especially the PS2. Even with the strength of the Gamecube, the first party was only enough to keep it afloat until the Wii came out. In the mean time, like they are now with the 3DS, and like they did in the past since the initial release of their portable line, they simply kept their handheld a great success.
Go back another generation: the N64 sold only about a third of the consoles that the PS1 sold. What did the N64 have? It had a decent first party line up, but most people that talk about the N64 don't refer to its great third party content. This was the first time Nintendo truly had major competition that wasn't a somewhat lackluster Sega console, and they found that their first party games just couldn't quite stack up to the likes of the notable FF7 and other third party titles that reached the PS1. Developers only released 387 games on the N64 compared to the PS1's around 1100. That definitely tells you where developer interest sat, and what it did to N64 sales.
The only reason first party saved the Wii was because of the type of crowd the Wii appealed to. It appealed to the casual market that ultimately only Nintendo could truly satisfy. Instead of tapping this market further, Nintendo chose to reenter the more serious gaming market, and they're finding that, once again, the third parties aren't on their side. Their strong first party content actually is hurting them more than it's helping them, since it scares off developers when their games don't sell nearly as well as Slightly Improved Mario Game #30. It attracts some when they see the system is selling, but even that isn't a grabbing point right now because the system isn't really selling.
The Wii U is currently on the path of being just another Gamecube or N64, and it isn't an unlikely outcome looking at Nintendo's history since other big names have established themselves in the gaming world. Nintendo needs third party exclusives. Multi-plats won't sell a system. They only satisfy current owners.