The Percom one came with a 1771 already plugged into it.
I asked why - isn't that chip a little expensive to provide, if the
customer already has one that they had to unplug to plug in the board?
One Percom rep told me that they tested and selected "the best" of the
1771s and supplied it, rather than have the customer using the random
quality one that they already had.
A different Percom rep told me that it was because they expected a large
percentage of their customers to "bugger up" the pins on their 1771 in the
process of unplugging it.