This article is not so great...
The story behind the Dazed and Confused song is more complicated. It was actually written by a third party and then reworked by the yardbirds.
http://en.wikipedia.org/wiki/Dazed_a...sed_%28song%29
Page did a large part of that reworking and then took his work with him when he left the Yardbirds.
As for the rest, there really are only so many notes and combinations of notes that sound good to the human ear. With millions of people writting songs, eventually some will sound similar. In the case of Stairway to Heaven, you have a simple and extremely common Am to D transgression. It's also used in the Who's Pinball Wizard.