I think it's more the fact that owners are being more optimistic of the cars value.
We just bought our 05 plate gti, a 5dr with 62k on, dsg, leather, rns2, sunroof, xenons, lux pack 1 and full history for under £6.5k - from stratstones with warranty.
It took us ages to find a car that was realistically priced and with a good spec, but when you look at the trade value in glasses guide the values are quite low.
ED30s appeal to those in the know (ie understand what is under the bonnet) who want a 5dr with a K04 as the only other premium option is a s3 sportback which only started more recently and are much more expensive. For that reason they'll be always more expensive.
It's all supply and demand led.