It's what America doesOn the assumption you don't think they would be dropping ads into things like throw ins or small fouls (because that would be nuts on so many levels), the only real large break in play are injuries.
At the moment, when a physio comes on, even if they are quick, you would EASILY have 10 seconds where you could throw in a quick ad with absolutely no risk to interrupting play, yet they don't do that now, so when do you think all these ad breaks are going to be shown mid-game because of a stopped clock?