If he's downloaded the shows, they should all be there. If he's talking about undownloaded episodes, TWiT only lists the most recent 10. This is because the RSS text file that iTunes pulls that information from would become unmanageably large. It would take up a considerable amount of bandwidth. Very few podcasts list all of their episodes. The RSS feed is meant to just be the most recent shows. All of TWiT's shows are kept at TWiT.tv.
To get the most recent shows automatically, click the "Subscribe Free" button. Then every time a new episode is out, it will be downloaded in iTunes.