You should really make them available to download even if you aren't logged in, it probably doesn't seem like a big deal but it probably turns away potential downloads by people that are lazy. I know it took me awhile before I decided to finally just register so I could download some maps.
Plus theres no warning telling you, that you need to register to dwonload the map. The first time i saw the ACCESS DENIED error I figured it was just a minor website problem, it wasn't until i finally decided to just register like above that I tried to download a map again.
It says "login to post comments" but it doesn't say anything about having to login to download the map.