My understand was that poorly coded apps with push/live enabled would open a push channel, but never close it again, so if you installed for example "Weather App 1" and it opened 1 push channel then uninstalled "Weather App 1" that channel would remain open and could never be used again, eventually users ended up using all the channels without actually using them (if that makes sense)
I have currently only 3 apps (excluding the 2 email accounts that use a push channel each) yet because I've installed and uninstalled other push apps in the past, I've actually not got any available push channels to open now, so any future apps cannot have push working (until I hard reset and lose almost everything).