Sorry for the delay. By Lab, I'm referring to this post:
http://digital-photography-school.co...-in-photoshop/ which links to a youtube video anyway. Nevertheless, as you said, #4 of ELAY's list covers the subject (I just checked to see if it was the same technique). The reduced images you provided, as you can notice, suffered from some "artifactism" in the sky. You should always check how subtle color transitions in great "surfaces" (such as a sky) behave.
Try and experiment with your photos.
Another tip: If you are on a Mac and use iPhoto, the Adjustments palette can be of great aid to do some color correction (I have rescued very bland colored photos with such a toolset).
Best of lucks.