RFE
I filed for my I485 sometime in April 2001. Very recently, I asked my lawyer the same question. She said that there was no "requirement" for tax/W2/pay stubs unless the INS asks for. She has been pretty good so far with her judgment so I guess I will just have to wait & see.
Though there is always a possibility that INS send an RFE for anybody, anytime or anything.