To explain more, iTunes (the Desktop App and the store) use the <itunes:summary> tag first, if that doesn't exist it uses the <description> tag in the RSS feed and lastly <content:encoded> tag (your blog post).
The Podcasts IOS App use (in this order) <content:encoded> then <itunes:summary> and lastly <description>.
Until Apple changes it (contact them to complain), it will just be that way.. Yes, it sucks
-Mike