1) My pfSense server is a laptop which is very old (purchased in 2000) and I wanted a design that was easy to swap out the laptop should it fail. I can swap the Linksys router into the edge of the network quickly if the pfSense server fails.
2) The laptop has two PCMCIA ports and a network adapter (NIC) fills each port. I could do more with multiple NICs and would have preferred 8 ports on the laptop. I didn't want to use a USB network adapter because the laptop uses the slow USB 1.1 interface.
Lastly, my preferred choice was to use a filtering bridge, pictured below, in place of the Linksys e3000. The filtering bridge would filter the upper portion of the network (.200) as DMZ servers while leaving the lower portion without filtering. The pfSense box only has two NICs so I would have needed an extra machine or a separate hub. Again, this design offers too much complexity for home use.