Another explanation might be an increase in Twitter spam. I can only speak for myself, but I've been getting tons a spammy followers over the past couple weeks. You'd think that the most popular accounts (like the ones highlighted in the article) would see the highest levels of spam, thus the sharp increase in new followers. I'm sure the suggested followers feature Ev mentioned plays a part as well.
This is what happens when your research leads you down one path instead of checking the obvious sources first. These people are on the list of suggested users: http://twitter.com/invitations/suggestions Twitter is suggesting people follow these people.
I'm not much of a twitter user but the uptake in the general public in the UK in the last two weeks is crazy - its gone from no-one to everyone in the space of a week.
Personally I think there was some kind of internal BBC briefing about using twitter for publicity - then the radio 1 jocks logged profiles all in the same weekend, started talking about it daily the week after and so started a snowball from the publicity.
I noticed a sharp increase in local Twitter usage on the radio here as well (US) a few weeks ago. That was most likely in response to Britney Spears' account getting hacked.
http://brooksbayne.com/post/79132853/the-newest-way-to-game-...