I definitely think in the last couple years the share of Nintendo in terms of software has dropped. This is also partly tied into the amount of new Wii hardware that Nintendo is moving. I think this is simply a matter of two very simple, straightforward things as opposed to any grand sweeping shift in consumer behavior:
1. The Wii is at the end of its console life cycle. Nintendo seems to be more in line with a traditional 5-year cycle with their system versus the longer tails and higher future-proofing of the XBox 360 and PS3 hardware. As a result I'm not too surprised to see Wii software and hardware slowing down.
2. The Wii doesn't have the third-party support that would traditionally hide/make-up-for the shift of first-party resources into new console development. As a result, this makes the petering-off effect even more apparent.
Also, as regards tie-ratios, I know it's not official, but Gamasutra has a decent enough rep that I feel relatively safe using their informed speculation as regards to tie-ratios:
http://www.gamasutra.com/view/feature/6350/npd_behind_the_numbers_march_2011.php?page=3
Good link, I think it seems perfectly trustable. Salient bit, per my previous hypothesizing:
"In the 15 months prior to that period (i.e. from October 2008 through December 2009), we estimate that the breakdown was 48 percent for the Wii, 32 percent for the Xbox 360, and 20 percent for the PlayStation 3. The key dynamic at play here is that Wii software unit sales dropped by over 25 percent from the first 15-month period to the second while PlayStation 3 software grew by 18 percent. Software unit sales for the Xbox 360 were basically flat between the two 15-month periods.
This is a point we've made before, and one that's worth making here again: Wii hardware and software sales are still at healthy levels, for the moment."
It's been nearly 15 months since this report, so I think you could posit another big percentage shift away from the Wii, despite it having the highest install base, while new software hits are still coming out regularly for PS360. This makes it a bit of a chicken-and-egg problem to me; did third-parties stop supporting the Wii because software sales were dropping precipitously, or did software sales drop precipitously because third-parties stopped supporting the Wii?
The article also possibly backs up my previous theory, that while console sales and software share dropped off, a sturdy core of Nintendo supporters was able to push the tie-ratio up over time, though helped by occasional cultural break-outs like the Just Dance games.
I guess I'm just not confidant that there's enough different about the WiiU's appearance and tonal presentation to lure enough third parties back to the table to give it another go-round for traditional titles.