As far as I can tell, the drop rate is the same for each node (with one possible exception--see below). I've tracked 35 different characters, total of over 8000 attempts. My total drop rate was 2781 of 8247, or 33.7%, roughly 1 in 3. Individual drop rates for specific nodes have varied from 22.2% up to 43.8% (counting only populations of >=50). Statistically, getting low total drops on small populations is more probably than on large populations, so this has to be considered when figuring out how probable a given result is.
With that perspective, of all the results for all the nodes I've tracked, I find that results from only 2 nodes fell below a 2% probability of occurring: Darth Sion (27.1%; 69 of 255; probability of getting this low or lower = 1.8% or 1 in 54), and Xanadu Blood (22.2%; 32 of 144; probability of getting this or lower = 0.13%, or 1 in 772). The first doesn't seem outlandishly improbable given I've got 35 populations (it's not that improbable to hit 1 in 54 odds after trying 35 times), but the second is either some serious bad luck or else the drop rate on Xanadu Blood really is lower.
Granted, I've only tracked 35 nodes, but of those, only the one seems improbable. I'm still collecting data on Xanadu Blood, so we'll see if my drop rate increases.
