Want to know why the Avalanche went after Greg Zanon? Per the Eurolanche (via Adrian Dater), Jan Hejda is having had wrist surgery that will put him out 4-6 months. That timeline could still get him back to start the season, but Greg Sherman is nothing if not conservative and cautious. Zanon is insurance. That's not to say that there isn't a logjam of defensemen, but as DDC aptly pointed out, this season isn't much different from the start of last season in that regard.
Here's the original article from the Eurolanche. I recall reading it when first published, but didn't think much of it because I figured Hejda would be back before the start of the season. The Zanon signing hints that may not be the case. Speedy recovery, Jan.
Update: I was totally right to begin with. Avs say Hejda will be ready for camp. I still think it may have been an insurance signing. Or a harbinger of a trade.