I doubt people will do a full systems change due to price.
Truer words never spoken. Price is about the LAST thing to enter into the equation if you are actually talking about the tools with which you make your living.
It took a true game changer like the Nikon D3 to get me to even THINK about switching systems. Several of the other Canon shooters in my area were looking longingly at the images the Nikon guys were getting in the crappy light situations, but nobody I know actually switched. Most people choke on the pricetag, and some of us who are heavy old-school manual focusers can't abide the idea of having to re-learn how to do it "backwards."
People like me who work in news/editorial/event photography should be in the ideal target market to switch to the Nikon D3 due to it's low-light chops. But, frankly, this area does not pay exceptionally well, so for most of us it's just too painful to consider dumping the 10 G's or more it would cost to switch even if you sell your current gear at a good price. And while the D3 is better in low light, Canon's are still quite good.
At the other end of the spectrum, the heavy duty commercial people who are raking in thousands per day don't HAVE to switch (at least not for the low-light capability) because they help themselves to light from a phalanx of Elinchroms. It may be a different story for hobbyists who may make their living in dentistry or lawyering, or the ones whose "system" is just a body and one or two lenses, but aside from that, there's not a whole lot of switching going on.