BABESH,
There are practical problems with using large value input resistors.
Let's assume that the resistance path to ground equals the input resistor, in an attempt to cancel the effects of the input bias current. You still have a problem with common mode input voltage. The bias current (Ib) of the op-amp will create a common mode voltage equal to Ib X Rin. Unless the input bias current is extremely small, this common mode voltage will exceed the common mode voltage rating of the op-amp. Also, with large value resitors, the sensitivity to capacitively coupled noise will be very high.
Regards,
Kral