HTC Sense UI may not be going to any Google branded phone. That means in Singapore, G1 will not be getting it (if HTC really DID release it). I guess one of the reason is because HTC may have incorporated Microsoft Exchange which does not goes too well with Google.
It is no surprise that HTC is breaking away from the Google branded phone. From the short history of HTC Android phones, only G1 (or Dream) is a Google branded phone.
Now, if you are still unsure of what is Sense UI, it is a new UI developed by HTC (just like how they develop TouchFLO 3D).
Click Here to See the Sense UI at work
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(source)