I actually agree with you in many ways. First of all, I'm not sure if any of you knew this, but Nintendo has never really been insanely successful before the Wii. Not since the days of the NES and to a lesser extent the SNES, have they been at the top of the market. During the SNES era, Nintendo was losing ground, and the launch of Sony's PS1 was a major blow. Even once Nintendo got their 3D console, the N64 up and running, they still never beat out the PS1 in terms of sales and user base. In the GameCube era, Nintendo was dominated by Sony and Microsoft with the PS2 and Xbox respectively. It wasn't until the Wii that Nintendo came out on top, and managed to break into a market other than their dedicated fan-base. It is wrong and generally ignorant to believe that Nintendo has always been king, even if you really enjoy their games.
Recently, Nintendo has made a few errors. The 3DS didn't have the best of starts, but it has come back, even to beat out the PSVita in Japan during it's launch week. It is now building and continues to build a respectable library of games, and receive consistent updates and support. However, the launch of the 3DS was far from perfect, and was plagued with issues such as the lack of a launch library, the lack of the eShop at launch, and the lack of a communication method between you and your 3DS friends. The Wii U, which was announced at E3 2011, was also not well received by investors, nor was it particularly well received by the gaming press and fans, who were confused and cautious about the new console. Here's hoping that CES will shed some more light on it before E3 2012, where the console will launch soon after. However, we all know that it won't. Nintendo also had a very lacklustre year for the Wii, with Skyward Sword and to a lesser extent Kirby's Return to Dreamland being really the only major titles, especially in the second half of the year. Third party support was no where to be found.
So yes, I would say that Nintendo is losing it's edge, but it's losing an edge that it never really had. While Nintendo have had their successes and failures, they have never really been the top of the competition since the late 80's early 90's. If Nintendo wants to keep their seemingly temporary position on top, they will have to do something special with the Wii U, and go above and beyond what the 360 and PS3 offer now, and what the inevitable sequels to those consoles will offer. From what Nintendo have showed of the Wii U up to this point, it doesn't really look like they are going to achieve that. Sure, they may catch up to the current gen consoles in terms of graphical capabilities, and maybe even online-based services, but what will happen when Sony and Microsoft launch their next consoles, which will have to happen in the next few years. Nintendo will once again be behind in terms of technology and what their console offers. However, despite this I think we can all agree that while Nintendo may not have the best hardware, the best third-party support, nor the best online services, they undeniably have always had, and likely always will have great games.