What's the deal with IR?

My bet would be that a lot of players are staying at their homes (a lot of which aren't in Indiana) and rehabbing their injuries.  It's a lot of stress to put on someone to make them travel to games, but you do see it.

Monte Reagor traveled with the team as motivation last year during the playoffs and he was on IR.

I think I remember a story last season about being on IR (from Vikings LB and ex-Iowa player Chad Greenway). I'm pretty sure he watched the games from the stands and didn't really have much interaction with the team, but he was a rookie that went down very early so he didn't have the same kind of relationships with teammates that a guy like Freeney does.

I'm guessing they can't practice or play, but I don't see any point in keeping them out of any other team activities.

IR is a product of the roster limits. A team can only have 53 players on the active roster, so when a player goes out for the season they would have to cut the player or have them as dead space on their roster without IR. I've seen it argued by a few different people and I agree that the roster limits, inactive players and IR need to go. Roster limits were needed before the salary cap to prevent teams from stockpiling talent but now there's a better system in place. If their weren't roster limits teams could bring in as many players as they could afford under the cap, these players could get experience and learn the team's system instead of bouncing around practice squads or not playing at all. It would raise the level of play from injury replacement players. Wouldn't it have been better if the Colts could have kept Luke Lawton playing all season and didn't have to cut a solid situational player/backup in Simeon Rice to fit Lawton back on the roster. IR wouldn't be needed because injured players could stay on the unlimited rosters. Backup/ special teams guys that aren't worth a dead roster spot for weeks, but aren't out for the season like Roy Hall, Dante Hughes, Victor Worsey, Federkiel, Seidman and Antonio Smith wouldn't have to sit out if they are healed up and ready to play (I don't know how injured those guys are but I'd bet a few will be healthy enough to play now or before the Colts are done with their season.