For one I don't really think that Super Mario 3D Land's really that easy as compared to past entries, from what I've been seeing. (Well frankly speaking the only Mario games I've ever played in my life are Super Mario Bros when I was a lil kid and Super Mario 3D Land which I just bought 6 hours ago.)
Both are equally awesome IMO.
Plus, about the thing that Ninty's screwing up by ignoring the older generation, I don't see that it's the case, at least if you're looking from the viewpoint of sales. Wii and the DS were pretty much one of the best-selling consoles in history ever, and with Ninty's targeting of the much wider demographic this time round I don't see how it's even leaving anyone behind in the dust. There's always games suitable for everyone. But most importantly, since this new approach at the target audiences work, why not stick with it? It's earning them hell lot of moolah anyway.
But yes, some parts of your argument are true. Like Metroid, for example. Keeps reminding me of Tomb Raider (yeah you know what I'm talking about)
And with Nintendo's attempts to retarget the more "mature" audience hasn't been too smooth now either. The 3DS nearly flopped, even though Ninty did its magic and it's now on its way to beat DS in terms of first year sales. But for the Wii U, industry reaction hasn't been too enthusiastic about its attempts to reconcile with the more hardcore audience.
Oh well, let's just see what the big N'll do along the road.