Pretty much the same thing...making asics costs money, using gddr5 VRAM chips costs a lot of money, and the bulk of it is reserved by nvidia and amd. Cost is prohibitive, you can't risk making an asic for a coin that might fail. We are getting scrypt asics after a loooooong time now, but we wouldn't have them if the amout of ram used in the scratchpad changed over time, wouldn't give the manufacturers time to bank on it.