Is an instrumentation amplifier design same with a standard op amp?
A instrumentation amplifier is more than just a opamp hooked up as a differential amplifier.  The inamp puts buffers in front of each of the diff amp inputs.  This presents a high impedance to the outside, and also eliminates the cross impedance between the inputs of a bare diff amp.

In theory you could make a inamp with three opamps, but in practise that still won't be as good.  A real inamp benefits from all the components being on a single die, which help in matching thermal characteristics and ballancing the gain of each input to get better common mode rejection.  Precision inamps go thru a laser trimming process in production to get the absolute and relative gains just right.