Just because you’re focussing on PPC advertising rather getting organic traffic via SEO techniques, doesn’t mean you can totally ignore building inbound links to your websites. Sure you don’t need as many but you do need some.
And, of course, not all links are created equal. Inbound links that are one way, ie that don’t involve you having to link back to the other site, are the ideal. Inbound links from thematically related sites are superior. For example, if you have a gardening site then an inbound link from a site about internet marketing is not as valued as a link from a site that supplies gardening products.