SyndicationFeed & SyndicationItem LastUpdatedTime

I'm trying to use the SyndicationFeed class to get content from a feed, but for some feeds it works ok but for others it doesn't.

For example, when I want to get feeds from http://www.alistapart.com/site/rss , the LastUpdatedTime has a value of 01-01-0001 for all feed items and the feed itself.
Is there something that i need to do? or is it maybe that SyndicationFeed doesn't support all websites to read from them all the information?

some sample code that i'm using :

var feed = SyndicationFeed.Load(XmlReader.Create("http://www.alistapart.com/site/rss"));var feedPosts = feed.Items; // here all feedPosts have the invalid LastUpdatedTime, but if i go to the website i can see that there is actually one