The bible would have an impossible time keeping up with actual market fluctuations. Every year certain notes would go up due to popularity, then go back down when the fad cooled, which ultimately would not be good for the market in general.
The Bible's editors have done a good job the last 20 years showing a small but steady increase in most notes even when market demand could have dictated larger increases. Remember the days when certain sellers automatically charged over catalog as soon as it came out?
In recent years a few notes have shown large increases, example *R/A, *N/Y probably due to pressure from contributors, but I'm not convinced sellers are realizing those prices.
The end user of the bible needs to know availability of every note. Right now, alot of notes sell for below book, making the book appear too high.
Some rarely found notes or certain issues in gem unc would sell at a premium over book, making it look too low.
If a note rarely ever is seen in gem how could it only be priced at 30-50% higher than unc?
The 3-tiered uncirculated pricing range is still in its infancy. In the future, the gem column should really rise exponentially for rare notes, and drop in the unc column for common notes.