a 99% FH or FB coin can be a fraction of the cost

I remember reading a piece written by David Bowers on the "Full Head" Standing Liberty Quarters.It essentially raised the question that I have been struggling with this week. The November event in Baltimore has several coins that interest me, a few of these are SLQ's. One coin in particular does not have an official FH designation on the slab, however it does have a fuller head than many I've seen slide by. In addition to the 99% FH, as David Bowers pointed out, it has other elements that only a super strike has...full rivets on the shield, a strong shield emblem with lines both horizontal and vertical...strong eagle feather definition all the way up to the under edge of the right wing. My point is, how did the head become THE MAJOR determining factor?..even so much that an MS66 of one coin valued at $2000 can be a fraction of it's lesser MS65 FH sister valued at $15,000? One coin is superior in every aspect except the head and is of far less value? Who decided that the head was the most important and that much so? For my money the MS66 with 99% FH at less than 1/7th the price would fit my collection very nicely. And just a quick word on Full Band Mercury dimes. Check out the price difference on a 1918-D MS65 and 65FB.....$750 compared to $42,500!!! Many of these coins that narrowly fall in one group or another are so close to being FB or not that it becomes almost a judgement call.Out of 9 people 4 may say yes and 4 may say no and then comes the $42,000 opinion of 1 person....hmmmmmm...those 2 little letters, whether FH or FB can be awfully costly, and they may not even be right...