Sony's CRTs have set the standard for the world for over 20 years. They are used in every professional TV studio, movie set, and editing room.
The major reason for this is the patented Trinitron tube design, which allows for a flatter picture tube with less edge distortion, a different kind of "mask" to fire the electrons through that allows more accurate color, and finer pixels for more precise lines and text.
Anyway, it is true that you only need a tuner built-in to receive over-the-air broadcasts OR unscrambled analog cable TV, and only the former will be an HD signal. All other methods of getting programming, especially HD programming, use an external box and will not utilize the built-in tuner anyway.
For example, a DirecTV HD receiver or TiVo will come with a number of outputs to connect to your TV:
- HDMI
- HDMI to DVI (if the only digital input on your TV is DVI)
- analog component video (red/green/blue)
- analog S-Video
- analog composite video
"Digital Cable" decoder boxes are similar, as are current "up-converting" DVD players and future Blu-Ray HD DVD players.
I wouldn't spend extra to get an internal tuner myself, but most HDTVs will have them anyway.
-Troy