I was surprised this wasn't mentioned in the article, but I have made several purchasing decisions for my company with the simple incentive to remove the "Powered By" branding, even though we weren't gaining anything feature-wise.

It makes an effective freemium model. Give all users all (or most) features for free. Then the ones that want to remove the branding will pay for that privilege. This way, the smaller free users are essentially paying for the service through promoting your brand. The users that don't want to promote you have a way to do it and will you pay you for that.