How useful is the wheel without roads? In terms of mpg efficiency, weight efficiency, and off-road capability, the wheel seems comparably less efficient than evolved legged locomotion. At least for the purposes that are more important for animals.
I suspect InclinedPlane was...well, thinking of surfaces other than inclined planes. Some terrain can be crossed with legs but not with wheels (of comparable scale). I assume he was talking about that, rather than making a quantitative comparison across flat surfaces.
I don't have any specific numbers, unfortunately (it's hard to find mpg ratings for oxen, for example). However, if you can provide an example of a 1 horse power wheeled vehicle which can take 1 to 2 passengers plus moderate cargo across more than 20 miles per day of rugged terrain including shallow streams and rivers and can be powered entirely by resources obtained in situ then I'll cede the point.