In my observation, the curse or pattern(whatever you want to call it) started in 2002 with Culpepper. The players on the cover before that didn't get hurt ; some did, some didn't, so I can't really include them in the curse.
Since Culpepper, every player has suffered in injury that has caused them to miss a game, with the exception of favre, who should've missed games due to his injury. It almost ended his career ; the media was talking about it all summer. It was a significant injury.
Football is a rough sport ; players often suffer injuries. Players also go through seasons and remain relatively healthy. Starting with Culpepper, no player that has appeared on the cover of madden, has been able to remain healthy for an entire season.
Until that happens, no one will convince me that the madden curse doesn't exist.