There hasn't been a 2D Zelda on a handheld or otherwise in 5 years, and in the last decade there was only one non-remake 2D Mario on a handheld. Bottom line: Staleness is relative, and very much subjective.

There's several reasons why it's logical from a business point of view for Nintendo to release games like Mario 3d, Zelda 3d and Metroid 3d, even though they sell less than Wii series and (some) 2d games. To understand them you have to look at the big picture, not each game in isolation.

Diversity is one aspect, and Nintendo uses it to make the consoles appeal to a wide range of consumers. Another way to this is making each game appeal to a broad audience, hence most games are e for everyone.

Another aspect is that Nintendo understands that the console needs its iconic games that stand out from the huge amount of mediocre (=good, but not spectacular) games. What those games are depends on your taste in gaming, some people see Wii Sports and Resort as those, some Mario Kart, some Galaxy, others Zelda TP, some even Wii Music. Without each of those games, a portion of the Wii install base wouldn't be there and buy other games, too.

So those games sell a lot of smaller games, and thus it's not only financially ok but necessary to have them. I think the fact that Nintendo hardly ever lost any money in this business even in last place and now accumulates huges piles of it in first place validates the correctness of this business model.

NSMBW is a horrible example anyone can put. It is a well established FLAGSHIP franchise for nintendo that almost always has amazing legs. Although Castlevania is a well established franchise as well, it has been on other systems and successful in the past. I wouldn't mind some sort of updated SOTN for the PS3 the same way they did with the GOW series. Granted, judging by some of the people I've spoken to online, it would be safe to say that a Castlevania of the QUALITY of SOTN would sell REALLY well on the Wii, but if they choose to go in the direction of some spinoff, then no. In that case it would only be successful in the DS.

That is just your opinion, nothing more. Opinion is not the truth. There are also many people who play 2D games just in short bursts, never in any other way.

2D Zelda was never more popular than 3D Zelda, not even on handhelds. Even TP sold more than 2D Zeldas except one.  Remember, Zelda: OoT is most sold Zelda, not any of the 2D Zeldas. So 2D doesn't automatically make it more popular than 3D.

Also, not all 3D Mario fans would even buy 2D Mario as incredible as it may sound. This is because fanbases are never exactly same. Not all SMG owners buy NSMBWii even if it would sell 3 times more. So killing 3D Mario would actually lose them more than keep making them. Even if those 3D Mario games would sell much less. They need diversity to keep as large audience as possible. Those people wanting 3D games would abandon Wii if they would axe 3D games completely.

Btw. SMG still sold more than any Zelda game ever released (2D or 3D). So I wouldn't call them bad sales.

Did the NES, SNES or Gameboys have the capability of going 3D? No.
Do the DS and Wii? Yes.
Do they have 3D gaming? Yes.
Why? Well, to make the most out of the console, naturally. It'd be plain stupid to only make 2D games for a console that can very well handle 3D as well.
Besides, as has been said as well, the 3D Mario games and the 2D Mario games are different genres, they cater to different audiences. Nintendo is all about getting as many people as possible to play, if they lessen their diversity they'd go straight against their goal.
No matter how you look at it, if Nintendo would stop making 3D games, they would limit their diversity. That's an undeniable fact.

Oh, and would you mind telling me how long it took for Nintendo to develop NSMB Wii from scratch, and how long it took to develop MG from scratch?

There's no shining example of 2D superiority, either.

Face it, Zelda has been at its biggest when it moved to 3D. Probably the best example we have is Virtual Console - guess what the top selling Zelda is? Even at double the price, Ocarina of Time beats out the original Legend of Zelda.

As for the other 2D games, Adventure of Link and Link to the Past, they are outdone by Wind Waker and Twilight Princess, respectively. 3D Zelda has sold better than 2D, and they manage to do so with smaller userbases. This is a fact.

As for taking multiple "FF6's" over Uncharted 2 or Super Mario Galaxy, I think that's a little misleading. I doubt it's easy to pump out AAA 2D titles like NSMB Wii. Sure, it'll be faster than the 3D titles, but it's probably been grossly exaggerated in this thread.

Anyway, in the end, Nintendo would be best suited between a balance between 2D and 3D, and releasing a larger variety of games. They can still make another 2D Donkey Kong, I'm sure that would perform well. Zelda and Metroid peaked at 3D, though. I know you (Avinash) seem to agree with Malstrom stuff, and well, even he thinks Zelda would be best 3D (with a more arcade-combat focus).

Beacuse you can't release one mario or zelda 2-D game very single year, in the end people will tire of them.

....So are you saying you don't think that 3-D Mario is getting made anymore? Is that what you're saying?

If so, I'm going to ask one of the admins if you and I can make a ban bet

LBP is 2.5D, with three planes of movement in the z direction for the PS3 and two in the PSP version. This is about the same degree of freedom in three dimensions as Doom had, and you wouldn't call Doom a 2D game would you?

That is a very ignorant comment. In addition to the Wii and PS2/P we have seen amazing 2d games from PSN, Wiiware, and XBL.