"One bullet, one kill" - isn't that some kind of sniper saying from the movies? If you're a professional botnet operator you're not going to want to loose control of your favorite botnet just because some damned whitehat managed to take down a single command and control (CnC) server.
With that in mind, you're also probably not going to want to build your botnet in a way that its growth is reliant upon a single infection vector or content distribution vehicle. The solution nowadays lies with the strategy of running multiple campaigns against your targets.
Just as political contenders running for office unleash a barrage of sophisticated and targeted campaigns to draw in supporters, professional botnet builders similarly unleash their own barrage of targeted campaigns - looking to sucker en mass their victims.
To understand botnet building campaigns a little better, I've thrown up a blog on the topic over at the Damballa site - Botnet Building Campaigns.