The wording is rather mild compared to manufacturers usually say and besides we know that what was written is not true. Every company that has independent service centers includes a recommendation to take any minor jobs to the shops as a bone to toss to shops for increased out of warranty work to compensate for the low reimbursement rates they pay. I used to have one of the largest pro audio service centers in the US and depended on those referrals because the 54 brands we were the warranty service for, we were paid less that the cost of repairs. That is normal and the shops do it because of all the referrals at full shop rate. That is the case with almost any repair field. That $100 cleaning if under warranty is probably $18 if a warranty claim is paid to the shop.
If the writing in owners manuals were followed you could only use Ford spark plugs in your Ford but that was resolved decades ago in court. Stan St Petersburg Russia