RARE ITEMS.
Otherwise known as not very likely to be found, and/or perhaps a limited number of them in the world. The concept that is failing to take hold here is that these are MAGICAL items (rare and wonderful). They are not simply workaday "gear" for the common adventurer of level X. Why is a rare work of art worth so much? Oh yeah because its RARE!
If some DM decides that these rare magical items are actually just gear then he or she can price them however. Pricing based on meta-game utility IS saying that this is just gear.
Actually, I'd like to comment on this.
The item might be rare in the campaign world and rightfully so, but there might be some rare items that the PCs eventually find in every single one of my games.
Why?
Because they are fun! I don't give a rats rearend if WotC thinks that an item is rare and shouldn't be bought or any such thing. I care about whether my players are having fun. The PCs and the campaign world does not exist except in the minds of the people at the table, so if there is something cool in the DMG and it brings laughter and fun to the table, by gosh it's showing up. It doesn't matter how rare it is. As DM, I'm there to enhance the enjoyment of everyone and I find that finding magic items, regardless of whether they are found in a store, or in a dungeon, or just out in the middle of a field, is FUN!!!

I think people sometimes lose sight of why these items are in the DMG in the first place. It's ok for some of this stuff to just be gear, as long as the players are having fun.