Traditionally the cover athlete for Madden has been revealed the same weekend as the NFL Draft. The general idea was to kick-off the promotion of Madden alongside the NFL Draft with the cover announcement being a major part of that. Even if not the same weekend it has usually been in the same general time frame as fans of the sport being concentrating on the upcoming season.
However according to Sports Business Journal (via First Cuts) that may not be the case this year. EA Sports is apparently reevaluating their marketing plans for the game and pushing back the cover announcement for Madden 2010 could be the result. Despite that I would still expect various promotional activities related to Madden 10 to occur throughout the draft.
One thing this does almost certainly eliminate is the idea of players bidding for the cover with the proceeds going to charity. After the first discussions of that the topic has never resurfaced and this news seems to solidify that the player is being selected in the same manner as has been done in the past.