why does the parallel resistors with voltage source can be ignored as well as resistors in series with current source in term of equivalent circuit?
In your equivalent resistance equations, you are missing the fact that a voltage source has impedance of 0, and a current source has infinite impedance.  Anything in parallel with 0 impedance still results in 0 impedance.  Likewise, anything in series with infinite impedance still results in infinite impedance.

To help convince yourself, try putting some real number on your top example.  Pick some values for the voltage, Rp, and R.  Now put different loads on the result and compute what the voltage on the load is with and without Rp.  You will see that Rp doesn't matter.  The voltage across the voltage source is the specified voltage, by definition of what a voltage source is.  Put another way, a ideal 10 V source always gives you 10 V, whether someone else is drawing 10 mA, 10 A, or nothing from the same voltage source.