My understanding is that the ETH and other algorithms designed to be run on GPUs have big memory and memory bandwidth requirements, which is what makes it more difficult (or less cost effective?) to implement on an ASIC.

LE. I see you meant NVidia should be making the ASICs. In that case, that's exactly what they're doing, isn't it? This CMP line is exactly that.

ethereum was especialy designed to be mined with gpu, i think asic or fpga will miss the memory size that gpu have.

The big draw of gaming cards is their resale value, when they become obsolete for mining they can be resold to gamers for significant fraction of their original price. Truly huge mining operations use ASICs anyway, but for medium sized farms gaming GPUs make more sense.