How much die space and power budget does double precision take on ATI hardware

[faxon]

So i was going through setting up my milkyway farm about a week ago, and one of my boxes had an open slot i was trying to fill. turns out i didnt have a compatible card for the slot because my HD4670 didnt support DP FP ops, and im not running win7 on that box yet so i cant use an 8800GT unless i downgrade to XP from vista. the whole process got me thinking though, why exactly doesnt ATI ship any cards other than their highest end models (38xx, 48xx/47xx, 58xx) with the ability to do DP FP ops? they claim it's because it takes up to much die space and uses to much power for it to be worth it on the lower model GPUs, but include it on the highest models because those are the ones that they also use for their compute model GPUs. if this is true, what impact does including it really have exactly? it would be really great if people could use midrange cards like the HD5770 for milkyway@home and other apps which require DP to run, but apparently ATI doesnt think these cards are worthy for some reason