LFG ICC 25 6.5 GS! Does this mean anything? Sure, they're looking for a group for 25 man ICC. GS? What is that? Oh, you mean gearscore, that thing that everyone hates.
Who hates gearscore? Well, for the most part, casuals do. Casuals obviously are left behind in the dust as new gear is introduced, as they're unable to find the time to obtain it. This gap only widens as content patches are introduced. "It's not an indicator of skill" is the biggest argument against this third party device. I'm sure no one can disagree that it doesn't accurately measure one's competence. Surely, bad players can get booted in a raid, thus preventing them from getting gears. On the other hand, players who know what they're doing can get screwed out of gear or can't find the time to raid regularly.
Okay, that sounds fine to me. However, in top end raid, be it Ahn'Qiraj in vanilla, Sunwell in TBC, or ICC (or Ruby Sanctum) in WotLK, maximum output from skill is automatically assumed and expected of all players. That being a given, the only variable that remains is gear. It should be obvious that a person maxing out their DPS with 4k GS won't match up to a person maxing their DPS with 6k GS. Therefore, how can gearscore be a bad thing?