Well, they have a reason to be. Nintendo could have been completely prepared for HD gaming, just by observing the failures and successes of MS and Sony last gen. Instead, they decided to continue to live in a bubble. Their system wasn't truly ready, their games/devs weren't ready, and their online infrastructure wasn't up to snuff. And because of the lack of power, they are getting nowhere near the 3rd party support of the PS4 and XBO, which helps fill in the gaps left by 1st party delays. Basically, they stumbled out the gate worse than Sony did last gen, but without the hopes of a recovery.
I think what also has Nintendo fans worried is that Nintendo has already teased its next system, which they are supposed to announce in full next year. My guess is for a 2017 launch. So, there's a chance that games may be moving to that system to round out its launch lineup. Basically what MS did with several 360 games late last gen.
