Grading: Abrasion Or Wear

You have just run into the difference between technical and market grading. Under technical grading wear is wear and abrasion is wear. If there is abrasion on the high points it's an AU coin. Under Market grading a nice eye appealing coin with abrasion on the high points will still sell for MS money so it gets graded as Mint State. The grading services use market grading but how likely they are to coin with slight abrasion Mint State will depend on the eye appeal of the coin and whether the market is strong or weak. When the market is strong there is a lot of demand for coins and collectors are more likely to accept a MS coin with "rub", but if the market is down they become more picky and the coin has to be "all there" and they are more likely to reject MS coins with "rub".

I avoid the whole headache and buy circulated coins. They may not rise in value that much, but I same a lot of money and can buy more coins.

Thanks for your replies, that definitely clears things up!
Especially with older Dutch coins (pre-1800) many if not most have to some degree a weak strike. In some cases this is only visible on the highest points, which can make it hard to distinguish from rub/wear. Knowing that some slight rub doesn't automatically downgrade a coin to AU makes the weak strike/wear distinction also less important. Good to know!

In the current marketplace, coins grade up to MS-63 with slight wear. As long as it is very slight on the high points and not in the fields, it can be MS-60 to MS-63. At 64, there really can't be any rub at all. I see coins in slabs that clearly have technical wear on them, but are mint state. It is most evident in some series like Standing Lib Quarters which are MS with wear on the knee, but not on the breast. Indian Quarter Eagles have obvious wear up through MS-63. I think the illogic of an MS-67 Gem becoming AU-58 with the slightest wear has become realized in the market in which wear is being considered only one characteristic of evaluating the eye appeal of a coin on a continuum from P-01 to MS-70.