Model S 60D->75D is + $8,500 Model X 60D->75D is + $9,000 Same platform, same batteries? Why is the 75 upgrade more expensive on the X? Also, is SAS "included" with the 90? Model S 75D-> 90D is $10,000. Model X 75D-> 90D is $12,500. The Design Studio claims "Includes Smart Air Suspension". This isn't including SAS, it's adding SAS. If it included SAS, it'd be +$10K. Maybe my comprehension is off?