Marriage still has some tangled-up benefits, Dave. I'm not too pleased about it, but it does. Joint tax filing is a boon to knotted couples, and then there are a handful of other legal gifts, like retirement-IRA sharing, Social Security benefit transferability, and even what I think is the worst: many hospitals still abide by next-of-kin legal designations.
The sooner those things go the way of the dodo and we can write our desired entanglements on a post-it-note, the better, but for now, it's the wedding that is so unnecessary, not the marriage itself.
After all, the ceremony, and the after party are mostly there for brides (and moms), not so much for anyone else. The marriage? Well, I already wrote that.