I couldn't care less that my credit union doesn't have any branches outside of my state. They refund all ATM fees anyway.
Many credit unions participate in a network so you could use most any other credit union's ATM as well. I had a credit union that used the Co-Op network so was near a fee-free ATM nearly all the time. I don't now if IAFCU gives refunds for ATM fees, but I see their network, CU24, is huge -- about a dozen ATMs within a two mile radius of where I am right now.
They say it against their rules.
I doubt they block everyone transferring to Mt. Gox, BITSTAMP, etc., so they probably considered the Pareto principle where possibly 80% of the dollars being sent are from just 20% of the customers and to shut those down. Perhaps their highly paid compliance people do this so that they can argue why their salaries and bonuses are justified (make some arbitrary rule that is easy to enforce, enforce it, and then pat yourself on the back for a job well done even though there was no valid reason for it ... buying bitcoins isn't a crime.)