Not sure about the double core models; but this 3 core is just a bin/fault testing reject with one of the 4 cores busted, and either enough of them had one of the 5 shader clusters bad as well or the total number of these isn't large enough to differentiate the part.
As for putting a bigger GPU on the 2 cores the problem is that it would push their price up; while 2 core chips are only making their way into the lowest end boxes. Also, as slow as he CPU is I'd be worried that with only 2 cores it'd bottle neck an 800 shader GPU.
Really? 2.1GHz?
Since we are talking budget, why aren't their dual or triple cores, with boosted GPU cores and higher clock speeds. Take the 100W with 4 CPU cores and shift it towards the GPU side. So you can grab more GPU or more CPU performance depending on your intention. Why not a 800 GPU core with a dual-cpu option.
Almost like a Phenom II X2 + a Radeon 4850. That might be something.
aka.
2 CPU cores - 800 GPU cores
3 CPU cores - 600 GPU cores
4 CPU cores - 400 GPU cores
Instead, you have 5 options all mediocre.