This is obviously a remnant of the "get more followers" past. Having 500k bots or autofollow accounts follow you is not a viable strategy. Also you compare apples and oranges, look for SEO writer or SEO + PPC and you get better results I guess. That said it's clear than in the SEO realm there are more people trying to game the system, any system. That's why I'm glad there are tools like Klout that do not only count the meaningless number of followers but other metrics as well.
Here is another tool: http://fakers.statuspeople.com (shared by Rand) to check the Inactive and Fake Twitter followers.
If there is a system people will try to scam it - just the way it will always be. The key is to look one level deeper.
Proof that fiverr gigs do deliver :)
I have a question is there a reason this page ( http://moz.com/rand/the-most-followed-twitter-users-with-seo-in-their-bio/) does NOT have a share button on it? I find that very odd... or maybe I'm going blind in my old age.
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