You need a multiswitch if you have more than 2 receivers. The guy probably put in the first diplexer so that he didn't need to run another line to the multiswitch. I personally ran 8 cables from my dish to my wiring closet to handle DirecTV, Voom and dual antennas. I can see why people want to...
A multiswitch is for two sat feeds and an antenna. This guy piggybacked the antenna onto one of the sat feeds. This is done correctly and will work. I ran 3 lines to the dish myself and redid all the wires they did at my house, but you want two sat feeds and an antenna going into a multiswitch...
I can pick up ABC here on my Sony HD-100 and my iTech Access DTV, but not on my ProScan PSHD-105, my RCA DTC-100, My Samsung SIR-T165 or my Voom Receiver. So, can I pick up ABC or not? I guess it depends on which receiver I am using...