think about it, even if it isnt instanced, there are a number of ways they could have slowly let people in. whether it's by raid accomplishments, challenge mode scores, and so on, there are several possibilities to allow entry without gold...so why let member #1 be some random guy with a ton of gold to burn?
a guild can pool gold and secure all the invites if they so desire. or crowd the ah and harass people, if you are vodka. then they can choose to only give them to guildies, or (and this will happen) sell invitations. which essentially makes this invite an investment, and not so much about doing the pve content.
is this really the best way to handle letting people in slowly? there are people who havent step foot in a raid when it was relevant, who will get first dibs merely because they have the gold. is that fair?