If you look at the number of posts in many of the "hot threads",
having a layout option to read all of them would just not be
practical (from a readability perspective, or from a performance
perspective).
With the activity on the forums, the I/O load on the servers would
be dramatically increased with a different layout.
Phil planned this site for both growth and ease of use, and it
shows in the forum deisgn.
Also, would you rather have Phil reviewing cameras, or changing
forum layouts (to a design that would probably end up being worse
anyway, for the reasons mentioned above).