Yes, Toad.
And yeah, the 360 version has six exclusive characters. The PC version will have seven, but there'll only be six in any given install. (The Wii version is probably going to have exclusive characters as well if they ever figure out how that's being released, so that's four purchases if you want to play as everyone - super-true fan!)
On another note, the 360 version is getting new levels as free updates, but the PC version will be getting a level editor that'll let you make anything you see in-game except boss levels; while the new levels for the 360 version won't be added for PC, they'll all be replicable in the editor. The best fanmade levels will also be added to the 360 version.