Another consideration is how late in the generation these products will be released ...
The earliest I could see either company releasing their add-ons would be for the holiday season in 2010 (around 12 to 18 months from now) and while there will be a few third party efforts for these add-ons at launch and through out the first year, most publishers are going to take a wait and see approach about throwing support towards these systems. A large reason for this is simply a numbers game, where there are (roughly) 80 to 120 Million Wii owners who are buying several games per year, 80 to 100 HD console owners who are buying several games per year, and 0 Add-On owners with unknown purchase habits. If you assume a 12 to 18 month waiting period before dedicating much support to these Add-Ons, and 12 to 18 months before the high support translates into a steady stream of decent games, this works out to these Add-Ons getting this support in 2013 or 2014. If you consider what happens if new consoles or handhelds are released in 2010 through 2012 (taking away third party support and consumer interest), and potential delays pushing this hardware's release into 2011, it is entirely possible (and in my opinion likely) that these systems don't have the time to build consumer/developer support before their consoles are taken off of the market.
