Shopping Paradise: Hong Kong?

Many people said that Hong Kong is a shopping paradise and many prefer shopping in Hong Kong than in Singapore. This is my first trip to Hong Kong and I fully agreed to that!
I always have this question. Singapore and US has a Free Trade Agreement. Why is Products from US selling more expensive than Hong Kong? and is a lot more expensive from the stuff I grab as shown in the photos:
1) Timberland Earthkeepers™ Front Country Cabin Cruiser
    Hong Kong Price: HKD$630 (~SGD$101)
    Singapore Price: SGD$199 (based on the online price)

2) Crumpler Messenger Bag The Complete Seed
    Hong Kong Price: HKD$869 (~SGD$140)
    Singapore Price: SGD$189 (based on online price and RED is not available in Singapore)

3) Giodano Reversible Leather Belt
    Hong Kong Price: 2 for HKD$199 (~SGD$32)
    Singapore Price: 1 for SGD$23 (Only have on design and is thinner)

4) Sports Bean
    Hong Kong Price: HKD$12 (~SGD$2)
    Singapore Price: SGD$3,30(according to online website but this is no longer selling in stores)

5) Honey Stinger Organic Energy Chew
    Hong Kong Price: HKD$17 (~SGD$2.74)
    Singapore Price: SGD$4.90 (MSRP according to online website)

I will be back again to shop..next time need to buy 25kg of check-in luggage back to Singapore.