In 3 years time marketshare will already be settled. If the wii has by far the biggest marketshare it wont matter x360 and ps3 will offer better gfx (x30 and ps3 wont be that great 3 years from now anyway compared to what we can do by then) because Wii is were the money is. Besides that the Wii offers something ps3 and x360 cant offer so even if everybody has the need for HD gfx there will still be a market for Wii.
Just because it would have a huge market share doesn't particularly mean software would sell better on the system than it would on any other..
Currently the PS2 has the biggest market share by a significant market but unless your God of War or a new FF game then your not going to get significantly hot software sales considering the platform is winding down in favour of newer, more novel ones..
By that time regardless of how large the Wii market is developers and publishers will still be spending big bucks on HD game content for PS3 and Xbox360 because the installed bases will be comfortably sustainable..
In fact I suspect that the diversity of platforms will create alot of specialisation in terms of platforms catering to specific tastes. Therefore if a AAA title like gears of war can sell over 3 million (and counting) copies in a seemingly limited 360 userbase then how much more will the sales potential of such titles be when the installed bases of the HD consoles reach critical mass..?
In terms of profitability of a platform (in comparison to last gen) I really don't think its as easy as saying "the platform with the largest market share will remain the primary focus of software providers" because I (and both the platform holders for tha matter) don't consider MS or Sony to be fighting over the same pie as Nintendo..
I think its a rather safe assumption to say that consumer uptake of the Wii is having (and is going to have) considerably little to no impact on consumer uptake of the Xbox360 and the PS3 and the only thing holding the two platforms back from reaching critical mass will be sales. Eventuallty they'll come down and both platforms will stand to represent a separate playing field to the one that Wii has and one that's equally as lucrative..
I suspect by that point publishers will be quite happy to spend big budgets on the "hollywood production level" HD games with massive selling potential (upwards of 2-5 million units for the best of them) and considerably (because they don't need to) to churn out AAA Wii games (with possibly equal to or less selling potential per title which would be offset by the publishers ability to spend more, to release more titles within a shorter time frame and keep the cash flows high)..
All in all I don't see this generation being as focused as the industry has ever been before with content creators spreading more of their resources across the three primary platforms (and across the two handhelds) in order to grow more than they've ever been able to do before..
What a sunny outlook..