Phase-shift oscillator (high pass configuration) why only 2 resistors to ground?
A quote from my previous answer given yesterday regarding the phase shift oscillator with series resistors: - 


  Your transistor circuit with series resistors is self biasing - the DC
  flows through several resistors back to the base and, due to negative
  feedback, the collector dc quiescent voltage will be roughly mid-rail
  on low voltage supplies.


The transistor base must be biased for this to work correctly. R and RXXX are normally regarded as performing this function. Also, either R or RXXX can do the job of the final resistor in the phase shift network. The final resistor in the phase shift network can be tied to any supply rail because the phase shifting it performs is on an AC signal and either supply rail looks the same to AC.

With both resistors fitted, the bias to the base is better defined but maybe both resistors together attenuate the feedback signal too much and cause the circuit to fail to oscillate.

This can possibly be remedied by increasing the collector resistor (also called R to add to the confusion).