Just wanted to add my $0.02 worth here.
All communication from the handheld (data communication) is handled by service books on the handheld. The two different web browsers (actually 3 including the wap browser) are associated with their own service book. The BB browser points to the service book for your BES, and the Internet Browser points to the service book for your Carrier.
This also explains why you can't use GTalk atm (based on the error message you are getting) you don't have the Google Talk service book. Check with your carrier to see if Google Talk is supported. If it's not, you'll never be getting the service book needed.
As for the North American BES with a Singapore carrier, if you browse with the BB browser, there may be a slight delay, but it's based on a lot of factors...the BES host's connection to the internet (for requesting the page, and communicating with the BB network), the Singapore carrier's connection to the internet, and your connection to the carrier's network. It'd kinda look like this...
BB > Wireless provider > BB Network > BES > BES get's page from the internet > BB Network > Wireless provider > BB.
If you use the internet browser, it'll look like this
BB > Wireless Provider > BB Network > Wireless Provider's Mobile Data Service > WP's MDS get's the page from the net > BB Network > Wireless provider > BB.
Some advantages to using the BB browser is if you require access to a corporate intranet site (one that you can only get from your computer at work) you can access these pages with the BB Browser but not the Internet Browser.
The language display is dependent on what language packs are available on the server that is hosting the Mobile Data Service. The Singapore provider has all the languages you need installed for their MDS, but a north american BES host may not have all the languages installed, therefore it doesn't know how to handle the pages when it downloads them.
And lastly, as for the IT policy (BES controlling what you can and can't do) think of it more as a set of rules that are pushed to the BlackBerry when it's first activated. Your BB now has a copy of those rules, so whatever you can do with the BES, you can do if the BES is down (obviously except email and bb Browser, etc). The handheld will always abide by these rules until a new set of rules are pushed down. Even if you completely wipe the handheld, those rules are still enforced.