[User9812]

Well, that's a bold claim, but let's see if Photoshop really is inefficient. I took the original iguana image from the Compressor site, and then used Photoshop save for web to bring it down to 250kb (same size as the after image from Compressor).

I picked a spot and zoomed in where it's easiest to see the artifacts.

http://i.imgur.com/Sf72oZq.png

If anything, I'd say the Photoshop one is better than Compressor.