We currently don't have the technology to automatically transcribe podcasts into text (good for the SEO on your podcast site) - But even if we did, how would it know that something is an advert as opposed to part of the show? Most of the podcasts I listen to have ads and in many cases the ads aren't just at the start or end, they're either a live read during the podcast or a cutaway somewhere towards the middle.

Maybe you're just not the target market for ad-funded podcasts.