Jason Lawrence emailed me about this yesterday:

In Outlook 2007, image security in emails is turned on and I have to explicitly tell outlook to download images, due to security concern.  I also use Outlook for my rss feeds, but images in posts are automatically downloaded with no security question.

1. Are images dealt with in the same way regardless of whether they are embedded in an email or an rss post

2. Is there an assumption that because you have chosen to subscribe to an rss feed, you implicitly trust all content posted and this is the reason for outlook not asking you to download images in rss feeds?

Point 2 is correct and why the defaults are the way they are but if that bothers you, you can change it in tools - trust center:

image

Thanks to Josh and Dan for your help with that one guys!