"Factory de-limit"

I know that some of the non-sport E53 X5's were limited due to their tyres, but at a qouted (alledged) top speed of 149mph for the 4.6iS I always thought that, that was the top speed due to the physics of pushing such a brick shaped car through the air.
Am I wrong, were they 'limited' to 149mph as this sellers advert would suggest?
What would the de-limited speed be, if it does exist?