Here are your options:

1. Robots.txt - http://support.google.com/webmasters/bin/answer.py?hl=en&answer=93708 - easy option.
2. Noindex tags - http://www.mattcutts.com/blog/google-noindex-behavior/
3. Removal request - https://support.google.com/webmasters/bin/answer.py?hl=en&answer=59819

I think knowing why you want the follower counts would help us provide a better way to obtain the data.

For example, I look at profile metrics/authority when I'm setting a new profile up in a specific vertical. BUT, I know that I can use Topsy's twitter search to identify those authoritative tweeple. They have a nice hover-over feature that will show you follower stats for each user talking about the search query. I can also use TweetAdder to do this manually. I don't need to slow down, neigh,  I would rather not slow down to record or even read a list of follower counts.

If you truly do want the data for bulk processing within a site, some sort of new tool.. then pulling it directly from Twitter may be the answer. It really depends.

In my ten years, I have definitely heard of this happening. It's a bigger risk when your SEO provider has a private network of sites.Heck, I have even heard of people holding this over their clients; "If you quit you will lose all your traffic/rankings."

It's really no different than people paying YP for a directory listing, they are billed for "Search Engine Marketing" monthly and when they stop, the link is removed.

I view SEO similar to web design/creative -- if you pay us, it is yours, you retain ownership and that is the way it should be.