Yes, I think that's right. If you start, then the insurance is in place, has to be paid for, and no refunds are possible. If, however, the whole day is called off, and noone turns a wheel, the insurance was not needed and you can have your dosh back.
I should think the MGP office is a hive of activity... everywhere here is suddenly "race-ready"! I'm waiting to see the first bale of the season... like the first cuckoo....