By enabling Mouse and Keyboard support for games on consoles, they'll literally open up entirely new levels of success for their strategy games.
Game consoles have been (deliberately) crippled for years by manufacturer(s) for marketing purposes. Console hardware is sold at a loss, and depends on software sales (a secret "attach rate") to make the platform profitable.
Add a keyboard & mouse to a console, users might stop buying games and just surf the net (or whatever) with them.
It's why the original Xbox was a such a disaster for Microsoft. Beyond the game piracy issues (which continue on the XB360), end users were running linux on them. An attach rate of "zero" became possible. Microsoft dropped the Xbox as fast as possible, and rushed the XB360 into the market - with all it's unresolved hardware problems intact. (Not that Vista's release was any better quality wise - MS reminds me very much of General Motors in the 80's, 90's and today's Toyota it seems) Such a pity.
The keyboard, mouse, (and piracy - sigh) are the only major advantages (thanks to DRM) the PC platform offers end users these days. If game console manufacturers added full mouse/keyboard support, and adjusted their business model to allow some profit at the hardware sales point - the PC as a game platform would be dead and buried. Or at the very least, marginalized to niche status. That is what I believe we see happening today in the video game industry.