A lot of people don't bother to check the spare. I check mine every month although it can be a pain at times in the winter months, but it's worthwhile. On my old cars with full size spares I would rotate in the spare tire so all five tires would wear down evenly. Compact spares can't be driven at highways speeds so it's utterly useless until you get a flat, and most owners only wait until then to realize it has no air, or as you mentioned, the tread has started to peel off!
My '99 Taurus spare has been used a few times over the years and shockingly enough, it maintains itself at 50psi. I only had to top it up with air once in the last 13 years. My 2 year old motorcycle tires have more cracks then the spare tire does!
'00 Dodge Durango - 5.9L V8; 250,000kms
'06 Pontiac G6 GT - 3.5L V6; 98,000kms
'12 Chrysler 200 - 3.6L V6; 47,000kms