I keep hearing about how badly Nintnedo screws up in selling the hardware but what really irks me is their abysmal software sales!

If you take a look at the platform totals under software you'll notice that the 3DS has ONLY mustered up about 130 million game sales so far. If we were to account for the rest of the systems lifetime software sales it likely wouldn't go above the N64 software sales! Almost all of the 3DS's heavy hitters are out and have had considerable amount of time on shelf yet the software sales are dropping fast so there are no reason to believe that it will get a large enough rebound to revitalize the game sales. 

As for the WII U that console will most likely not beat the DREAMCAST in software sales! The WII U's total software sales currently stand at around 20 million but the dreamcast has around 65 million in software sales. Smash and mario kart will probably only move around 5 million units each so that will likely bump it up to 30 million but how are the rest of the titles coming out on the WII U going to have a meaningful effect ? At best I can only see the WII U reaching just over 50 million!

not quite sure about 3ds ,but WIi U? When your system is doing that poorly, you cant expect the software to do that great.

When hardware numbers suck, software numbers will also suck.

I think software on handhelds sells less.
The WiiU is selling badly so its software sales are obviously low.
The Wii's games sold very well.

Handhelds never have had high software ratio. 3ds and Vita both have almost the same according to this site (3 if I'm not wrong) and they sell a good amount digital.

As for Wii u, right now is not so high because the big games are not out yet, but it will most likely end up with similar ratio to snes and n64. That's the most it can get with almost zero 3rd party support. Responding to your question, their sales are not horrible, are good enough for them to make profit.

Funny, GTA 5 alone outsold the entire Wii U library. ^^

Don't own Wii U so cannot speak to that system's software sales, however owned a 3ds since launch and about half of my 80 games for the system are digital so I'm sure we would see better software numbers if we had those numbers as well instead of just the physical copy data.

Because they aren't selling horrible.The big games Nintendo releases still sell quite well considering their respective install bases.

The WiiU isn't mentioned much because it's not surprising. No one has any expectations for it in the first place, it's exclusives are actually pulling off pretty good numbers when considering the install base. As for the 3DS, it's mentioned from time to time, but they still aren't bad sales. Certainly the 3DS is a shadow when compared to what the DS was pulling in, but it's not doing badly in it's own right.

Instead, since neither of them are worthy of much heated debate alone, people would rather compare the failure of the WiiU+3DS vs Wii+DS and proclaim doom to all who shall hear.

Funny, Mario Kart Wii outsold the entire PS4 + X1 library. ^^

See how pointless this comparison is?