Nope, no difference really. Devy writes all of the music, and there's no connection in terms of genre/style/whatever. Epicloud and Addicted might sound vaguely similar, but Ghost, Ki and Deconstruction are all as different as Devy's music gets.
Like seasons said, the DTP was originally going to be those first four albums, and it was literally a project focussing on Devin Townsend, it was meant to exhibit separately four quite distinct styles/moods that make up Devy's music. Sounds like the label pushed for that name to be retained.
I've no idea about the use of the Devin Townsend Band moniker.