This is a private airport. I have driven by a private airfield on the way to my home town for years. It was basically a farm field with no lighting or marking and a power line right over the middle. The owner apparantly landed and took off under the power line. Do you think he needed a NOTAM? Please understand that requarements for private airports are (at least in some cases)non existant.

Also from the AMA letter.

"On the date of the incident the association hosted a by-invitation-only full-scale fly-in"

So this was invitation only so nobody could land except those invited who could have been told all of the details needed. So I don't see a legal requirement for a NOTAM, but not to say it was not a bad idea.