As Platinum myself, I seem to have better results with the US properties than the Asian ones.

For the past year after making Platinum:

1)HI Express Seattle: Suite after asking
2)HI Chinatown/Financial District San Francisco: Executive room after asking
3)HI Hong Kong: Executive room with breakfast (for one person only) after asking
4)HI Singapore: Deluxe room 1st stay; Superior room 2nd stay; both only after asking. Said they don't upgrade to Executive floor.
5)HI Guangzhou, China: Assigned high floor room, said they don't upgrade to Executive floor
6)HI Macau: High floor standard room after asking, said they don't upgrade to Executive floor.

What's their policy? On their website, it's written that Platinums are upgraded to Executive rooms at HIs and Club rooms at CPs.