First of all, i think this should be posted at the stickied Buyer's Guide thread above.

Now to your queries,

If thats true, MS will release asian version/ US version/etc at the same time or just for us version 1st?

Like you said, it is based on an unofficial news plus it is just a rumor. And moreover the date of release is not known so as it is whether US or Asia version of the console. Usually it will be US version first and then Asian. But when they change from the 1st gen SKU to the Falcon, if i am not wrong US and Asia changes it almost the same time.

Secondly, i would like to know registering SG account better or US account, whats the differences?

US account usually has the better benefits over SG accounts. They will get demos, game contents and other LIVE marketplace which is exclusive for the US region only. And the Microsoft points is region locked so you for an US account you will need to get a reload card from the States while if your account is SG, you can just get it locally, no hassle.

As far as i know, proxy wont enable you to download contents exclusive for the US. Just like how futile my efforts were in trying to get the Gears of War free maps.

Of course it does.
The falcon is personally thinking a good enough console.
Only a very minimum of people actually gotten the 3ROD from falcon sets.