http://www.wowpedia.org/Algalon
Algalon can only be accessed if at least one member of a raid has obtained the [Celestial Planetarium Key] or [Heroic Celestial Planetarium Key]. Players have a one-hour window to defeat him per lockout period, starting upon first initiation of the encounter.[1] Blizzard has sardonically referred to him as "Algalon the Raid Destroyer".
http://www.wowpedia.org/Sinestra_(tactics)
Sinestra is a heroic-mode only boss in the Bastion of Twilight, described as similar to Algalon the Observer in Ulduar. She is only accessible after Cho'gall is defeated.
As a playerbase we love hearing about the exploits of famous guilds and the hardcore on each server love racing for that server first. Seeing a new boss is awesome. Being one of the few and the proud that get to see the really cool exclusive stuff is a huge rush, but also a barrier to regular players who feel shut out because they don't have the skills or time or want to put in the effort to get in the top raiding guild to see the cutting edge content while it's still current.
So what do you think? Should they implement more, exclusive rewards for the few who are in the top guilds - or let everyone access it eventually with an ICC-buff system?