All, I am thinking of upgrading my current Linksys router to the Airport Extreme, but I have a question. It looks like Time Capsule, offers all of the benefits of the Airport Extreme, plus the addition of a HD. So for $120 more, I can get Airport Extreme PLUS 500GB HD? is my understanding correct? Is there any functionality that the Airport Extreme provides that TC does NOT provide? Thanks so much in advance.