ah yeh the m40 has always got a wide selection of buses from heathrow and gatwick plying the route day and night - very very popular.
I think the only thing holding oxford is the fact that the terminal can only 100 pax tops at any one time according to something i read - so not sure how they can attract anything more than an eastern or flybe type operation
Wonder why no-one has ever operated plymouth-oxford-edinburgh for eg or another route dropping in there?