That hardly seems like much of an explanation. Look at the old protocols Pidgin and other clients of the time (e.g. Trillian) spoke -- AOL, MSN, Yahoo... those

That hardly seems like much of an explanation. Look at the old protocols Pidgin and other clients of the time (e.g. Trillian) spoke -- AOL, MSN, Yahoo... those didn't run over HTTP. More importantly, the companies did respond by changing the protocols; the client-writers kept up all the same. So that's not something that's different between then and now.