Ok really not a scam, but silly.
The whole thing plays into people's superstitions. They offer you the ability to renew for 2 to keep a "13" off your plates. Well guess what? You can't renew your safety inspection for 2 years to avoid having a "13" on your windshield (yes, I just got back from getting my inspection done). I guess nobody thought this through very well.
I was born on a 13 so as superstitious as I might be, this is one thing I don't worry about.