Does my podcast need to be listed in the iTunes store for people to subscribe to it?
No, anyone who visits your podcast page can subscribe to it in iTunes by clicking the "Subscribe in iTunes" button in the right-hand column. They do not have to visit the iTunes podcast directory. If you want your show to be listed in the iTunes podcast directory, you need to submit an application to Apple. Please understand that Apple is solely responsible for deciding which podcasts are accepted into the iTunes Store podcast directory. If your application is rejected by Apple, we cannot help you. For more information, visit the iTunes tab of your Podcast Settings
Useful Apple iTunes Links:
Submitting Your Podcast to the iTunes Store
iTunes Podcasts Help Page
iTunes Store Customer Service