I think celebrating it on a personal level is fine. Expecting others to recognize it isn't fair - unless it has been made clear all along to close family and friends that a particular date is an anniversary.
A wedding is a particular moment in time that someone can mark on their calendar and say, this is when the lifelong committment / marriage began.
For people who choose not to or are unable to get married, I think it is perfectly acceptable for them to celebrate some sort of anniversayr (ie date of lifelong committment), as long as they hold it out from the beginning as the date.
Does any of that make sense?
Denae