Hence why there's this little mental policy as a referee (for me as a Hockey referee, as following the rules to the letter says that any injury means a 5 + Game Misconduct gets applied)... Unless it looks like a brutal check that an injury is probably, don't call it unless ambulances show up.
In football, if a player is (or looks) injured enough to leave the field, they get substituted by another player, how exactly is that different to Rugby?
Yeah, but you can't force a free substitution with an injury in Football. I'm pretty sure that if you've used up all 3 switches, you don't get to substitute the injured player, and will have to continue with 10 players instead.
I've never heard of that before, then again football isn't a contact sport while rugby is, so you're not that likely to see more than one or two injuries in a football game, while you're likely to see more in rugby.