Stranded Booing of teams not kicking the ball out when a player is injured isn't a Reading centric thing, it happens at a lot of games. Most fans are idiots and don't know the rule change has occured.
This was intriduced last season and plenty of teams still kicked the ball out from what I remember, despite being told to leave it to the ref.
Personally I was calling for either side or the ref to stop the game to allow Oster treatment. It would be a bit different if either team was in the midst of a flowing attack but we'd already repelled their initial attack and they were just keeping possession by passing along the back four.
The ref is instructed to stop the play if he considers that a player is seriously injured. That is a bit ambiguous but more often than not a ref stops the game to allow treatment if the player goes to ground, and in Osters case I think the ref should've stopped the game as he made an effort to continue but was obviously in serious pain at the time.
As for the general boo'ing of opposition players, I don't think Reading fans are much worse than most other sets of fans for picking out players for needless attention. We don't see it much against our players because we're a little club who nobody really has anything against yet.