It's not really so much different, once put in perspective. That resistor is a tweak to more precisely align equalization of the lower turnover. It affects mainly the 50Hz corner, which has little affect on equalization accuracy in the midband and treble. Mostly, you'll notice it as a gain change (~1dB overall). It also puts in a slight boost in the bass. Really, when you're working with 100k resistors and plate impedances, it's not so much. Hard to explain if you don't understand the intricasies of network design.
Think of it this way, the government could increase your taxes by a factor of ten, but the resulting national debt would not budge. Whether or not this resistor is 1 ohm or 10k ohm, it makes very little difference in the outcome. You'll get far more variation just by rolling tubes.
jh
