Hmm, interesting about the ten cars. I'd have to agree with a previous statement that it is so that there would not be too small a cap, particularly for larger and extended families where the household could have 4+ cars between them. Also, it is useful for a small business which has a small fleet of cars, such as a pizzeria. To me, ten seems to be reasonable cap, as well as being a nice, round number.
What is the VAT tax anyways?