On the Jason-3 mission, several times the spokeskids said that this is the last time we will hear the T-13 readiness check on a SpaceX webcast.
For example, at 27:23 they say:
...this is going to be the first and last time you are going to hear a readiness poll come on the air for a SpaceX webcast.
They did not say why. Why will they no longer allow us to hear the poll?
The go/no go poll is the last major hurdle before the launch. If one of the polled stations says 'no go', the launch will be delayed.
If the rocket is full of subcooled propellant, that delay means the propellant will warm up and start to expand. They want to avoid that, so they decided to move propellant loading to after the go/no go poll, which means the poll ends up at T -30 min, before the webcast begins.
The current version (Falcon 9 v1.2?) uses subcooled propellants. Jason-3 used the last F9 v1.1 rocket, which didn't use subcooled propellants. This meant they could start loading earlier, and have the poll later: having a delay after loading the propellant isn't as critical in this configuration.
