Well I think most people don't realize the change in return policy from 30 days to 14 days exists, as we all here do.
Plus the majority of iphone sales are generally pre-orders and 1st day sales...the big hype days.
So VZ takes the the day the most iphone sales are on and hopes to wipe out the majority of return.
Just take a look at the dates. Iphone released on the 10th and in 14 days her comes the Thunderbolt on the 24th, but if you wait until the 24th you actually are at 15 day and are expired. I'm sure the clock started ticking for the pre-orders as soon as they shipped. You don't think VZ shipped all the phones by mistake?
Yes, a smart person would not wait until the last minute but most people are procrastinators and they are betting on that.