Anderson and Bones draw really well when the public believes their opponent has a shot and will usually do pretty good to good with any legitimate challenger. I don't think the latter would apply to Rashad and Chael as champs they don't have an aura about them. GSP just gets ridiculous numbers in canada he really isn't more or that much more popular than Bones and Anderson in the US.
He has been a name for a long time. I think there are still way more GSP fans in America then there are Bones fans. Anderson is probably the most popular fighter in the US still. But both GSP and Anderson have longevity on their side. They have been at the top for pretty much the entire post TUF boom.