Well, it is actually true. This doesn't only apply to office ladies, this applies to students as well. Hong Kong really is all about designer clothing. An expensive, brand-name watch will get noticed. Same for a suit, a dress, etc.
As for what to wear at work - I don't know since I've never worked before (still a student), but if you want to deal with the humidity as well as the ice cold air con in the office, maybe try going for a long-sleeved blouse. Or perhaps just bring a smart-looking jacket - I see a lot of office ladies either wearing some type of blouse or wearing a jacket. It seems to do the trick, and it looks smart and stylish.
Oh, and as an interesting note, the "designer brand" rule applies to students as well - you're generally required to be in style whenever you're outside the house. Lately, I see even little kids with tops above their belly buttons, rofl.