As others have observed, the Golf 6 is a bit of an anomaly. There has been some debate about whether it was face-lift or a new model. Although based heavily on the Mk 5, Volkswagen fundamentally re-engineered the car to make it easier and less expensive to build. It might be better to call it the Golf Mk 5.5. That said, with so many sheet metal changes, that investment has to pay-off, so we should expect a 4 year replacement cycle, not the usual 3, as if it was just a regular mid-life facelift.
I don't know where you get your information about a new GTI by 2012, Horney, but with all due respect, I think you are being somewhat over-optimistic. I have no access to inside information on this, but i do read the German car mag, Auto Motor und Sport. One of their lead writers, Georg Kacher, also writes for the UK's Car Magazine. He says late 2012 (MY2013) for the new Golf and 2013 for the new GTI (MY 2014). I found him to be very reliable over the last 20 years.
The 3-door A3 coupe will debut either late this year or early 2011. The 5-door A3 Sportback will debut a year later. A new Golf usually follows 12 months after a new Audi A3. However, given that sales of the current A3 are so uninspiring, the launch date may well be brought forward. Since Audi is launching an RS3 version of the current A3, this will be allowed to sell for at least 6 months before a new A3 model comes along to replace it.