Both iTunes 7.x and Safari 2.X don't have a problem with this feed. Apparently both are robust enough to deal with the issues the validator brings up. Is your RSS reader having a problem with this feed?
The "errors" would not be hard to fix, but the Signs of the Times technical staff may be (and most likely is) too busy with other things.
Perhaps you could help out and fix the xml file for them (since you brought this up)?