In actual fact, things do get cheaper... If you buy something for $10 now and you sell it for $10 three years later, these future $10 will be cheaper than today's dollars due to inflation so you will have lost money. If the book value for a coin remains the same for several years, the catalogue which lists it is basically saying that the coin is getting cheaper in REAL money even though the numbers remain the same in NOMINAL dollars.
The values in the future guesstimate columns are denominated in today's dollars, so you should keep the above in mind when interpreting them. To simplify an example: coin X is worth $10 now. Next year's value for it is listed as $9.90. Does this mean we expect the coin to be selling for $9.90 next year? No. We expect that it will be selling for $10, but these 10 future dollars will have the buying power of 9.90 of today's dollars.
Yes, the same consideration applies if the future value is listed as higher than today's value. In that case, the algorithm expects the real value to go up - even beyond inflation.