Its one of my pet peeves.
Strangely when I bought my jeep it had a 30'' spare (flat), and 31'' tires on the ground.
within a cpl months I had a sidewall fail on one of the 31's so I put 5 new BFG's on it (stuck with the 31'' size due to me being too cheap to buy a lift.)
I'm so much happier with it since the tire swap. I say proper spare tire, or no spare tire.