There are a few guys in the NFL that are absolute lynch pins, not just to the success of their organizations but to the success of the individual performers who depend on the star to achieve their own great heights.
No one epitomizes this MVPness more than Peyton Manning. Just ask any fantasy owner who drafted Manning, Reggie Wayne, Austin Collie, Pierre Garcon or Dallas Clark - also known as about half the owners in your league. In all fairness Manning's own stock had been sliding steadily over the past month, but in many cases he still went as early as the 2nd round. And Garcon and Collie weren't necessarily considered top level guys at the receiver position, but if you knew Manning was going to call in sick for the first who-knows-how-many weeks you would have let those guys slide even farther.
The real victims here (besides Manning owners of course) are the poor suckers who took Reggie Wayne and Dallas Clark in the early rounds. Wayne is by all accounts still a top 10 guy and Clark is easily a top 5 TE, with Manning. Without Peyton he's just some guy named after a crappy TV show. I suppose that's not entirely true, Jason Witten shined last season under the horrific reign of Jon Kitna simply because Kitna was forced to constantly check down off his primary reads unless he wanted to get pulverized. Perhaps there's hope for Clark. But I'm guessing Reggie Wayne owners are inconsolable. And I don't begrudge them that emotion.
On the flip side of this debacle, of course, are all the owners who wisely didn't draft those Colts and now get to play watered down opponents until such time as Pey Pey rejoins the fold. I personally get backups twice in the first week of the season and I couldn't be happier.