The safe bet is that for (at least) the next 2 game/years (NHL/NFL 2008+2009) the XBox 360 will have a larger user base in North America than the PS3; on top of that the XBox 360 also offers a much lower cost of entry into the market (core $280, Priemium $350) than the PS3. All in all this means that it is likely the XBox 360 version will sell better and thus it makes more sense to spend the extra money optimizing the XBox 360 version.
On top of that I believe Microsoft has a better understanding on how important Madden (and other EA sports titles) are in the North American market; they probably are far more willing to send their engineers on the "Long" flight from Seattle to Vancouver to help optimize EA's games.







