I've upgraded my laptop from 2gb to 4gb actually, so it is possible to compare.
Didn't really browse around to check the best deal with ram, but I got my extra 2gb for $150HKD at the same store I bought my laptop, which I do know could have been a bit cheaper if I spent that extra time browsing.
The other difference is Video Card. 5850 has better performance than 6550 according to Computer Games on Laptop Graphic Cards - Notebookcheck.net Tech
The current exchange rate is 1CAD to 8.22HKD. So if you times 8.22 by 760, you'll get 6247HKD.
The laptop I got is bought for $5100HKD + $150HKD ram, coming out to $5250HKD.
That being said, online businesses may be a bit shady and often go through the tax evasion route. So lets assume they avoided the whole tax deal. Your computer will come up to $5333 with no tax added.
So $5250 and $5333 is around the same, but my 5850 video card performs better, so in the end Hong Kong's cheaper even when you evaded the Canadian tax. But we haven't included price of shipping and 10+ day of waiting time if you choose the most economical shipping method.
Dell is United States brand laptop, it makes no sense if it's cheaper elsewhere.
Have you seen the Alienware M14 from Dell? It costs $999USD but $15000HKD.
IQAir from US? $800USD but $11000HKD.
They're clearly overpriced. Not the typical electronics anyone here but people with too much money would ever buy here in Hong Kong.