People arnt dissapointed that its not as good as the 360 version so much, they are dissapointed because it doesnt look that good to them on PS3 in its own right and doesnt stand up as well to its peers on the same console.
90% of their target market won't notice the image quality differences. It had no effect on the sales of Halo 3 or Alan Wake or GTA4 or RDR or who knows how many other upscaled PS3/x360 ports so it won't have an effect here either.