That doesn't make any sense as an explanation for changes in the crime rate. If the quality descriptions were relative to each periods common expectations, then -- while it would still be desperately in need of support -- it would be a not-implausible conjecture as to a potential contributing factor to the effect it sought to explain. In absolute terms, is just a complete non-sequitur.

It's sloppily written. I expect that the increase in quality of what is on the market has moved the average buyer down. Thus, today, there are fewer $1500 TVs available for stealing than there were in 1990 (there are likely many more $500 TVs though, so maybe it wasn't a good example). Anyway, setting that example aside, I still have the idea that stuff is worth less today.