Apple has made changes in their latest iOS updates:
For iOS5 and below:
Videos from a podcast are no longer accessible via Music > Videos. Instead you now have to launch the "Videos" application. The PM Podcast only has a few video episodes, but in order to find them please go to the home screen of your iPhone / iPad and click on "Videos". You will now find the video episodes in here.
You can now find all podcast including PrepCast, PM Podcast, PDU Podcast video webinars in iOS6 application and can directly play them from here. Note that this application comes pre-installed on new IOS6 devices but you have to manually install it if you upgrade from a previous version.