Here's the word from Bridgestone Technical Dept.
When bike manufacturers are developing a new model they have approximately 3 years during which time their test riders will be able to determine what pressures in their opinion, best suit solo and (if different) pillion riding. They are also generally only working with two tyre manufacturers who will become the original equipment (OE) suppliers. Bike manufacturers usually launch no more than three new models a year.
Bridgestone has approximately 4,000 different tyre approvals in our fitment guide so, as with all other tyre manufacturers, we obviously only have limited time to test each bike so we test for the one set of pressures that work well whether solo or with a pillion. It would be irresponsible of a tyre (or bike) manufacturer to recommend pressures that did not give optimum stability, and higher pressures lead to greater stability. If we were, due to the aforementioned time constrictions, to only recommend pressures for solo use and then a rider took a passenger along without increasing pressures, and suffered the consequent instability that may occur, it would be the tyre company that would be held to blame.
The higher pressures we recommend are perfect for commuting, touring, motorways, general riding and pillion use. The only area where you could possibly increase grip by reducing pressures is solo sport riding, and then not by a heck of a lot.
One other point - we are recommending pressures that our test riders have found best for our tyres on, in your case, a 999. Ducati have never tested BT010s on a 999 and because of the different way each type of tyre behaves, what's to say that Ducati's recommended pressures will work with our tyres?
By the way, we used a 999 as one of the bikes for our recent BT-014 launch and they suited the bike perfectly. The BT-014 is the tyre that will replace the BT-010.
Bridgestone UK Motorcycle Technical & Sales
Now wher did I put that tyre pump