Ed, take a look at this link.
http://www.woodshopphotos.com/albums...lion.sized.jpg

I did a quick sketch for you. Cutting the mullions this way would give
you a decent glue surface. Although I didn't draw it, (I guess I could
do it if you want) you could make the glass stops which hold the glass
in as continuous lengths crossing the joint and joining the short
pieces together this would add some stiffness to the assembly.

In the photo you linked to, the mullions are mitered on the outside
and the glass is individual pieces. Doing this would make it a bit
nicer if a pane got broken. You only need to replace the one pane and
not all the glass in the door.

It would also make the door slightly lighter due to the reduced amount
of glass.

Hope the sketch helps.

Dave