It is often true that the simplest reason for something is often the correct one, but that is not going to stop me from speculating wildly about the reason for the delay in shipping the tv.
Reports are starting to surface that credit card authorizations for pre-orders of the device are starting to be processed. This is normally an indicator that the merchandise in question is close to shipping. It looks like we are not too far from the first un-boxing and disassembly photo-sets being posted online.
There is a disturbing incomplete, unrefined and un-Apple feel to the new full-screen Cover Flow in iTunes and the lack of integration of those features into Front Row. At the same time the interface features demonstrated during the tv unveiling are not found in either.
So I think that the delay in shipping the tv is because the interface is being updated with Cover Flow type features, including better song selection features when sorting by album and nifty little features like scrolling for long song titles and the index letter indicator when scrolling at speed.
I'm hoping that there will be an announcement of updates to Front Row and iTunes co-incident with when the tv starts reaching consumers. After all this is going to be like having an ipod next to your tv, and it should be just as easy to use.