It's not the "paying to swap back" part that stops high-end raiding guilds; they did double-switches for the heroic Darkshore warfront and the alliance's "against overwhelming odds" pvp quest when it had a higher ilv than anything else for a couple weeks before the quest reward got nerfed. It's the community; the groupthink is that alliance = casuals, horde = raiding, so if somebody wants to become a raider, they're advised to join horde, seek horde guilds, and even move to the big raider servers where the top 100 guilds operate. Lots of people do. So when a top 100 guild wants extra people to expand their roster for a few raid nights, there's plenty of interest and attendance, right there. On alliance, getting a raid team together is a little trickier, because it's like the spanish inquisition.