"For instance a "Rockettes." To accurately grade one you would have to have a quantity to compare and I do not think that you could get 10 of any rare strike together in the same room."

Peter; Please let me point out that the graders/slabbers would not need multiple pieces of your example of the Rockettes silver strike in order to grade such a piece ..... nor would they need multiple pieces of the famous 1804 Dollar to assign a grade to that rare coin. They are looking for common characteristics such as, wear; boldness or weakness of strike; toning; eye-appeal; depth of lustre; hair-line scratches; fingerprints; cleaning; etc. They don't concern themselves with quantities minted.

You asked; "Would you slab a $15 Luxor strike, when they are a dime a dozen?" The slabbing companies are currently grading and slabbing many of the common State quarters issues dated 2001 ... which are worth a heck of lot less than the $15 price you have suggested for common Luxor silver strikes ... and they are making a pretty good buck for their efforts. That's the whole point. The slabbers don't care about the WORTH of what they are grading/slabbing. They depend upon VOLUME, and turnover, whether it is rare or common.... and the more coins, chips and strikes that are submitted to their "services", the merrier and fatter their bank account accrues.