I agree that any one or two or even several milestones reached early mean nothing in and of themselves. I think LOTS of milestones reached early can be an indicator of GTness.
I think Ruf helped me personally because she offers concrete groups of milestones that work together to indicate just how "serious" the giftedness is. If the milestones indicate level 4, that's a different scenario than if they indicate level 1 or 2. I thought I had a level 2 kid; the milestones said he was a level 4 kid. That opened my eyes, and they needed to be opened.
I don't think her levels are the final word on giftedness, anymore than I think one test is the final word on giftedness. But I think milestones are one more tool that can be useful in seeing kids as completely as possible so that their needs can be met. More tools are better than fewer.
The danger I see in milestones is if they lead people to think that a given child is *not* gifted because s/he didn't do everything early. That's problematic.
As for the article, at least they gave the kids an extra year. Usually they say everyone catches up by 3rd grade...