I found another existing promotion here. Seems like if one purchases a J class ticket under this promotion, it is not eligible for miles or GUP upgrades as well. It is so confusing, who will read fine prints as well???

http://www.thaiairways.com//offers/s...hai_ann_en.htm

8.Economy Class : No mileage accrual ,
Business Class : Normal mileage accrual.

9.Limited seats per flight.

10.This promotion cannot be used in conjunction with other promotions including all upgrades