The rough economy continues to wreak havok on web companies. Yesterday, the online music discovery service Pandora was forced to let 20 employees go, founder Tim Westergren explained in a company blog post. This is 14 percent of Pandora’s workforce being let go, as TechCrunch notes.

The obvious conclusion is that Pandora is cutting costs to brace for a slowdown in ad sales, which is the service’s main source of income, but in the post Westergren says:

“Moreover, our ad sales are growing so well that, not only did we not make any reductions there, we need to continue to hire more.”

Westergren also says that listenership is “growing rapidly,” mobile growth on devices like the iPhone is exploding and that the service is close to a resolution of the Internet radio royalty rate, which threatened to bring down the entire company.

It seems that even companies with everything going right for them are bracing for the worst.

Other web companies with recent staff cuts include the Internet search startup SearchMe, the adult-focused social network Zivity and the social network hi5.