Single Rail Op Amp Input

I have been studying the schematic attached with much confusion. At the input stage I am seeing VB applying 4.5v DC offset to the Op Amp through a 1M resistor.

Surely the voltage drop across this resistor would mean the Op amp wouldn't receive 4.5v bias?

I Understand the 1M resistor sends the input to a default state when nothing is connected and I understand that the op amp needs 4.5v DC to allow full swing between 9 and 0v, but the way it is applied in this schem is confusing me.

Base upon praondevou's bias current values, the drop across the 1M resistor would vary from a typical 0.15V to a maximum of 0.8V which is probably not enough to significantly affect the op amp operation.