Why is there a parallel input resistor for the Maxim device?
The only thing i can think of is that it allows ithe input capacitance to discharge through it once it's stop being driven.
EDIT: I also thought that outputs were supposed to be low resistance and inputs are supposed to be high resistance to ensure loading of the output doesn't occur?
There is a small input leakage current (up to a microamp, according to the datasheet), which can flow, towards the Vcc or ground lines. Hence (I presume), an equivalent input resistance can be calculated. I'm NOT familiar with how IC designers calculate such things.
But I presume the worst case input leakage currents (and input capacitance if frequency is involved, i.e. when it is input impedance), are taken into account.
I think usually (especially at room temperature), the leakage currents are considerably lower than the datasheet limits.
As you said, outputs are usually suppose to be low resistance and inputs high resistance. Hence the (old) terminology of fan-in and fan-out. Which older logic technology would more frequently talk about than today. Eg. It was usually required/desired that a ratio of at least 10 to 1 was maintained.
I.e. One output device can drive 10 input gates/devices.