There actually seems to be a trend heading away from that. Where Pioneer used to use the same cards in their Elite lines as they did in their commercial products, they have now turned away from that as well, you will find that Panasonic 50" plasmas have more color depth in their home products than they do in the 8uk series of plasmas.
This indicates, that while the glass may be the same and come off the same assembly line, the actual video cards and graphical capabilities of these cards are now being heavily optimized for home theater use and that people will get more benefit out of actually buying the home theater model instead of the commercial model for hundreds less.
Add to that, the commercial model won't have features such as an internal ATSC tuner, CableCard, speakers, etc. This may not matter to some, but how about the HDMI port? That typically isn't there either. So, you pay a bit more (couple hundred) to add the HDMI port to the display.
I don't consider home theater products of the same caliber over priced - I believe they charge you appropriately for the extra features they are adding.
I personally am looking forward to when 2-way cable cards are finally out and you have a DVR built into your 50" plasma (or 42"?) and can have full Tivo functionality, yet all the simplicity of just turning on the tv and watching it when you want with zero external boxes.