Exactly. For one, if an HTPC / DVR backend server does the tuning and/or capturing, it allows you to integrate multiple diifferent broadcast sources (OTA, satellite, cable, even iptv) into a collective pool of recorded content and under a single unified program guide and navigation environment. Not sure how many people use cable and sat (my dad does, never did understand why), but the possibility is there and I think there are a greater number that might be interested in adding local OTA feeds to their current source. Or better yet iptv sources as they mature.
Secondly, it allows you to have centralized capture of all incoming signals and easily distribute them throughout the house. You get something like DirecTV or Comcast's "whole house DVR" but better. If there are only going to be 3 typical users at any one time, you only need 3 tuners... but you could access those tuners and/or stored/DVR content from dozens of different rooms/locations.
And this is especially attractive for people who use WMC7 or MediaPortal or in the future XBMC where stored media and captured/real time content are integrated under one GUI environment. In fact, there's already a plugin for XBMC that effortless transfers MythTV recordings to your media library, gets artwork and descriptions, and allows access via XBMC's content driven navigation.
Bottom line... I'm just one of those who in the past has had 6 or more different sources and ten remotes lying on my coffee table (that later went to one difficult to use and a couple of original "just in case" remotes) who would rather not have a stand alone DVD player, Blu-Ray player, Sat box, FM tuner, DVD changer, CD changer, etc. Each having a different looking menu, so even if you program a universal remote to operate them all, you (and more importantly the wife, children, guests) still have to remember how to navigate the menus and controls for each of them. Give me one pretty front end that allows access to all recorded content and incoming live streams of music and video, pictures, security camera feeds, all of it... from any location in the house, all looking and working exactly the same.