I'm not 100% sure why you can't do this with a high quality JPEG, but I honestly have only ever shot in RAW with my Nikon.
I suspect the changes made in the tutorial to the color s with color balance and hue adjustments. But I'm not sure.
Either way, I think the article is a good illustration of enhancing existing qualities in a photo with a program rather than garishly changing something.
Digital Photography VS. Digital Art.