I think you're confusing what 16x9 means. Most people don't fully understand what 16x9 means and what is it does and doesn't do. 16x9 is the aspect "ratio", the vertical height of the picture as opposed to the horizontal length. It has nothing to do with the size or resolution of the picture. A couple of common resolutions that 16x9 come in is 720x480p (DVD) and 1080i (broadcast TV) When 16x9 HD movies or programs are broadcast for TV they are sent in 1 "resolution" or size, not in 5 or 6 different "resolutions" or sizes. However, HDTV sets come in several "resolutions" or sizes. A 60" widescreen HDTVs resolution will be different from, say, a 32" widescreen HDTV. But Television Stations broadcast in only 1 resolution. That's where the HDTV set's software comes in. It takes the "Native" resolution of the broadcast and converts it to the resolution of the HDTV set. All widescreen HDTV sets (whether LCD, LCOS, Plasma or DLP) have "Picture" and/or "Zoom" modes for doing that very thing, converting the "Native" resolution (whether from DVD - 720x480 or from broadcast - usually 1080i ) to the resolution of the particular widescreen HDTV you have so you will have a 16x9 "ratio" picture that fills your screen properly and people and objects are not squeezed from any side. Some HDTVs do it automatically (default) and some will display the "Native" resolution (a 16x9 display that only fills maybe 2 thirds of the screen) and let you adjust the picture mode (resolution conversion) manually to your liking. I have a 32" LCD HDTV widescreen that has a resolution of 1368i and a high end HDTV widescreen projector system with a resolution of 1280i on a 120" screen. The 32" LCD displays the 16x9 in the broadcast "Native" resolution and I have to use the pic/zoom mode on the remote to fill the screen. My projection system will take the same 16x9 HDTV broadcast and automatically convert to the projectors 1280i res and properly fill the screen whether its set to 70" or 120".
Anyway, what I am saying is that the unit records in the native 16x9 "aspect ratio". Whether it fills your TVs widescreen is dependant on a couple factors, the resolution of your TV and whether it converts the boadcast resolution automatically or you have to do it manually with your "Picture Mode" on your remote. In other words, its not the recorder that "letterboxes", its the TV that does it. If a recorder is not capable of recording in 16x9 it won't record in widescreen and set it as letterbox, rather you will get a 4x3 aspect ratio (a square box) picture with people and objects squeezed. I'm sure you already knew most of this, I just couldn't explain it without going into detail.