Glad you brought the subject up of "Genuine" and "Aftermarket" service/repair items, this is an area that has collapsed into farce, and needs to clarified by manufacturers
A short while ago i had to replace the rear pads on a Mondeo Estate that was 14 months old and covered 20,000 miles. When i took the OE pads out they had Lucas on the back
Now if i bought the pads from my local dealer, they would be classed as "Genuine", but if i bought them from Camberley Motor Factors, they would be classed as "Aftermarket"......but they are both supplying Lucas Pads!!!!
This is where the whole "Genuine" con trick falls down
Surley as you rightly state, if you are buying parts through one of the buying groups who only deal in OE quality parts, then why should you have to pay a premium for buying the same product from a dealer
The manufacturers and dealers know their days are numbered for supplying "Genuine" service/reair items, so they are all jumping on the bandwagon to supply us with their own brand of "Aftermarket" parts though their Trade Clubs