I suppose it depends on how you view spending time with people and celebrating even minor milestones in others' lives. I have been invited to a total of two anniversary parties, had a separate one thrown for me (surprise), and am aware of a handful of others.
Just like pretty much everything else in life, how anniversaries are viewed (private affair vs. reason to celebrate outwardly), is going to differ from couple to couple, circle to circle. And I don't think there is anything wrong with either. For me personally, going to celebrate another couple's anniversary is no different than celebrating someone's new job, promotion, getting a professional certification, etc. It's just a reason to go out and say "Hey! We're friends. I like you. You're happy right now, so let me come here and be happy with you. Cheers!" If it's not your thing, it's not your thing...but it being a turnoff to you, doesn't make it wrong. I have never given someone an anniversary gift nor have I ever received one (from someone other than my DH). Not to say that other circles wouldn't consider them gift giving occasions, but that's not a universal thing...not mentioned in the Dear Abby letter, and not, IMO, really relevent to whether or not a potluck is appropriate.
So potlucks. They are a type of party. Afternoon teas are a type of party. There are also formal dinner parties, dance parties, sales parties, business parties, etc...and what is asked of the guests and provided to the guests can vary a million different ways within each kind. And I just don't see what the significance of the reason the party was organized to begin with plays into it. What is required, I think, is a clear communication of what guests should expect to bring and what they will receive...and I think there are good ways to host and bad ways to host. But arbitrary rules of no potlucks for anniversaries...I don't think so.