I bought my car from Stratstone Derby at the end of January, and I paid for it at the time of collection. I didn't actually examine the car before I transfered the money, but I guess the option was there as the car was under a cover in the show room. The hand over took around an hour.
I would not be happy having to pay the balance up front then having to wait weeks for it to be delivered. It was not so important for me to have an 08 plate, so I imagine the dealership was not so busy which resulted in a better service.