But it sounds like everyone is invited...which seems crazy, maybe even tacky.
I wouldn't post a wedding or baby registry online, but I don't think posting about an upcoming wedding (or even post wedding) is rude simply because everyone online isn't invited. I mean, when people get engaged, a lot more than just the invitees to the actual wedding know about it...and it's pretty obvious that following an engagement comes a wedding. I seriously doubt that everyone operates under some polite fiction that if they weren't invited, it's because there was no ceremony/reception. And I would hope that everyone on someone's friend list, doesn't expect that they would be invited to every life event simply due to Facebook status.
The thing about Facebook is that we document our lives...and we invite people to see that. If I couldn't post or talk about anything on Facebook if everyone wasn't invited, I'd have nothing to talk about. I get together with friends and we take pictures and post them on facebook. I go to birthday parties that end up on facebook. Weddings, christenings, showers, etc. All there. And I know that the 300+ friends that some people have weren't all at the party.
I really think there's a big difference between say a group of four friends having a conversation, where three of them talk about plans that they are excluding the first from and someone posting about wedding plans on FB. The former, I think is rude and where the etiquette rule applies. The latter, not so much.
But, as for the open invitation to the wedding and the wedding registry...is it a gift grab? I don't know...but it does seem off. Who has the budget to say they can accommodate anyone and everyone that might want to show up? And who would even want to issue an open wedding invitation much less attend one of someone you barely know?