It does show up, when you view the podcast on the iTunes directory, or even on the itunes podcast web site, click the "i" icon and that's your itunes summary.
For different reasons, PowerPress added an option called "feed maximizer", it takes posts 11 and older and cuts down the content and removes the <content:encoded>, not because of your reasoning, but to make the feed size smaller (loads faster and gets updated more often). the consequence through is that you loose meta data for your long tail and thus makes it harder to find those episodes in searches. We've noticed where we use it that it indirectly helps with SEO, less content getting copied over the web.
I would check wordpress.org plugins directory there has to be a plugin that removes the content encoded. I do know in WordPress options you can turn on/off whether the entire blog post is put on content:encoded, but that's a blogging feature, not podcasting specific.