My OS X screenshots with both cmd-shift-3 and cmd-shift-4 have always defaulted to PNG out of the box. I've been on board since Tiger and on two different machines.
Same here, and my screenshots have never been blurry, either. I have no idea where the author got the info that "by default the screen-shoot format is a made as a jpeg set to resolution 60".
My guess? The guy took a full-screen screenshot, opened it up in Preview in Auto Size mode, and was surprised that it looked fuzzy when shrunk to fit on his display.