It's not my case, but I've heard from some people that they got on Facebook because friends where organizing events there and not having an account meant not being included in these events. This might be a case where it's "ridiculous to even consider".
In the end it depends on the ways people use it. If it's the only channel for communication, then you have to be in it.
You just have to be cool enough so that people start thinking "how can we organize the event so that X will also show up". Problem solved :-)
Another question: do you really want to meet people who would exclude you from an event just because you don't have a Facebook account? Friends don't exclude friends...
You seem to assume it's on purpose. When almost everyone in your circle has a Facebook account, it's easy to forget that person X or Y doesn't (usually depending on how close a friend they are with them).
Personally, I don't miss my account, but I can understand why others can.
In the end it depends on the ways people use it. If it's the only channel for communication, then you have to be in it.