You're right in that asking prices don't seem to be falling off much, but I believe that that is purely sellers being stubborn. I've seen certain properties for sale at the same price for ages, there is a large (by Sutton standards) 4-bed detached place on Castlewood Grove for £349,995 and it's been for sale for at least 9 months. There's another property that backs onto the lawn at £495k, that's been on the market forever. A friend of mine has a bungalow on Sutton Road up at £400k, and after stripping a measly £10k off it a few months ago, refuses to ask a penny less.
It's my belief that sooner or later people will click onto how ridiculous their valuations are, and bring them back in line to a more reasonable figure, one they might have a chance of selling at.