Can someone please explain this attenuation setup?
My first thought is that although 4x 11.8 ohms in series/parallel still equals 11.8 ohms, you get 4 times the power rating and, if the resistors are high tolerance and/or low drift types (like the 25pp/degC used on the right-hand attenuator), finding a resistor that has this "spec" at 4x the power rating may have been impossible.

A second thought is that 4 in series/parallel as the series pass element of the attenuator may also give more options when it comes to making the attenuators "natural impedance" something other than 50 ohms, say 75 ohms (as may be used on the same PCB but in a different product). 

The attenuators above are for 50 ohm systems - I did a quick calc to confirm the left-hand pi attenuator is 2.03dB when 50 ohm loading is used on the output (right hand side of the circuit) and it looks the same for the right hand circuit.