Opto-coupled EIA-422 receiver (understanding suggested circuits)
It seems that R1 in the first circuit and R3 in the second circuit play similar roles: limit the current of the protection diodes for the reverse polarity and limit the current for the LED's for normal operation until the transistor based current limiters kick in.

R1 and R3 do not have to (and should not) have particularly large resistance - they do have to be physically large to limit overheating in case of a high reverse voltage.