Just developing GPL software for a certain part of an embedded system doesn't necessarily require all other hardware parts to be GPL'ed as well, just as your BIOS being proprietary doesn't violate the GPL if you're running Linux.
Would be great to see a fully open-source phone some day. I believe OpenMoko was striving for this goal, too.
Part of the problem is that they haven't shipped Froyo officially. But yes, manufacturers, even HTC, have been up to 6 months late delivering code as required via GPL.
Are we missing even Eclair source? I know Froyo and GB have changed things enough with some of the drivers that forward porting has been harder than expected... but if Eclair's source is missing, it seems the proper response is some sort of campaign to get Samsung in gear. I do think that HTC responded to GPL complaints when they had held out so long on releasing their kernel mods.
As I said elsewhere in the thread, vendors don't have to release source for drivers (kernel modules); AFAIK every Android phone uses proprietary GPU drivers at least. So even if a vendor released all the source that they're required to release, that may not be enough to create a custom ROM with a future version of Android.