Cause it looks like butt and makes the car look like butt.
IIRC, the place the makes the plates, or the coating, for washington warranties them for 5 years. Somewhere they determined 7 years is good so you are right, they seem to be stretching the time.
Yeah, you do get a new number, by default. Which irks me because the new numbering system sets off my OCD big time. The old system is 3 numbers then 3 letters separated by a dash. The new plates are 3 letters then 4 numbers with no separation. Its so uneven and *****.
Actually, now that I think about it, I think new plates are the same as regular renewal too. But there is an option to have your old number reprinted on the new plate for a fee. I think that is what Im thinking of. I think if I get to 7 years Ill definitely have my number reprinted. I like it. Its cool because it has an 'X' in it. I dont know what I do when I get a new car and have to get one of the retarded looking plates.