[Mark McLeod]

The WPA kiosk keeps track of who hasn't setup their robot bridge.
FMS keeps track of who hasn't successfully connected by the end of practice day.
FMS knows who was bypassed in each match, but not why.

Those kinds of stats aren't part of the published official record though, so FIRST has them, but I don't know if they get uploaded to the HQ servers, or are still traveling the world stored in the individual field systems.
More detailed notes are usually hand kept by the FTAA, because of the variety of problems and causes that are usually tracked.

All the fields I worked delayed matches as long as necessary to get all robots working. Long Island didn't start a match with a robot that failed to connect, unless a robot issue was identified that needed time-consuming repair, dead batteries, etc.

I have those stats for Long Island because I worked it, but not for other events.
The hand records maintained by the FTAA every year are really useful for follow-up with the teams in the pits (and for debunking conspiracy theorists from the stands).
Mike (our FTAA) keeps track of robots that didn't show up, robots that failed on the field and the reason (sometimes supplied after a pit visit), connection issues, unusually low battery or bad battery conditions, slow packet transit times, and anything else unusual that needs to be followed up with the team in the pits.

At the end of the day on Thursday we make everyone who either had connection problems or who hadn't connected yet, come to the field for a special connection party. That's true for each of the events I've been to so far this season (NJ, WPI, LI).
There's always one or two robots that still don't come...