Interesting. These "best" lists are always a bit problematic, and debatable.
I came out in Seattle, lived there 5 years. Yes, it's very gay friendly in most respects. It also has a hostile police force that has a long history of abusing the gay community. Apparently this ranking didn't take that into account.
Enjoy being out in Seattle, but be wary when you see the police approach. And don't expect them to do much if you get assaulted by homophobes, because they really don't care. City politicians and senior police brass put out nice PR about reform, but the rank & file police are as gay-hostile as they ever were. It seems to be culturally engrained in the Seattle PD, and no PR is gonna change that.
Minneapolis and St. Paul are also gay friendly, without reservations. My time there was always good, I even led their enormous Pride Parade on my motorcycle (with 60 other bikers) for 2 years. Problem is the rest of the State is much less so. Just 20 miles to the northwest is Michele Bachmann's Congressional District, as homophobic as you can get, with perhaps the highest gay teen suicide rate in the US.
Stay within the city limits and you're OK. Venture into the suburbs and beyond and you may be dead meat. An oasis in a sea of gay hatred.
I'm sorry, I can't see Atlanta at all. That's nutty. They leave greater Fort Lauderdale off the list for Atlanta? Right there the list is a big FAIL.
The balance of the cities I could accept as friendly, though I think it omits at least a few.