Metrolinx is currently crafting a strategy to integrate it's commuter services into all the municipalities of the Greater Toronto Area
And while good GO access only exists for some neighbourhoods, you are seeing people who work downtown choosing suburban areas that have GO, around the Lakeshore West and East lines, and also near Yonge in North York, Thorhill and Richmond Hill.
Also the areas around Yonge, and to a lesser degree, Lakeshore West are somewhat more expensive than average, it doesn't seem to be the case for Lakeshore East.
As for people moving into the core at a rapid rate, its a bit difficult to compare to some American cities, many of which have areas that have been leapfrogged by development near job centres but are now being developed into higher density suburban subdivisions.
It might not be high density condos but it still represents a desire to live closer to the central job centres.
Also I don't think all that many people are driving into downtown Toronto or even the core in general. As of 2006, 66% of jobs in Toronto employ residents of Toronto, not the suburbs. Those remaining 34% amount to 429,000 people, of those probably about 100,000 take GO transit, mostly into downtown. Maybe 50,000 more take other transit into Toronto?
That leaves maybe 280,000 that drive into Toronto, but presumably much of that is to suburban jobs, which make up about 60% of Toronto's total.
One of the things that surprise me somewhat is that Malton and Rexdale aren't more desirable, seeing as they're very close to the biggest suburban job clusters around Pearson, Condord and Bramalea.