That's cuz fos, pos and hor offer 219-232ilvl items, which are typically better than the low-tier raids you mentioned above. That's why angrylol and I advised you to farm those three dungeons and not bother with the aforementioned raid instances. People still do them but only for the sake of gathering achievements and/or tmog.
RS is an end-game raid. Idunno why you haven't seen anyone spamming it in /global and /trade chat yet, but I can assure you that players continue to form pug raids for it. The GS requirements for that are higher than ICC, that's why I didn't mention it in my post. I thought that you were interested in closing the gap between your character's gs and the average IC player's.