In the original Telegraph interview the manager said they made 17% net return on buses, only 3% on rail.
Rail operations are franchises / service provision contracts and if things go really badly different to what's envisaged, there's the sharing of the loss by the
DfT» through cap and collar, so the risks taken are actually very low. So it's only fair that the rate of return on a franchise that's running about right should be fairly low too. You could argue (and there is evidence) that this arrangement stifles the desire to take any risks what so ever when seeing a good opportunity to improve services, but that's another story for another thread.
Bus operations are much more truely commercial ... a higher risk taken, and more chance to loose a shirt or two, or to make significant gain.