Hi Hevans, it is indeed done intentionally and is a great point of discussion in the automotive world, my personal preference is to have the front wheel turned in and most clients want this as they wish to show their wheel more than the underside of a dirty tyre. However there is an older generation of auto photographers out there that state that the rules say a wheel should be straight at all times.
My personal feeling to this is that I don't remember seeing a 'rule book' anywhere and I'd rather do it differently to everybody else anyway. As a result my clients love the way I pose their cars and lorries and I have never been asked yet to set things any other way. Hope this helps and makes sense, there are in truth lots of 'conditions' on a shoot not least things like which way the screw heads should sit, vertical or horizontal, and things like tyre makes and window positions.
He's a shot that took a lot more than a few turns of the wheel to sort out.

Promotional shot of a fully restored Aston Martin DB6. This is quite possibly to date the most difficult shot that I have ever set up. Shot in England it took 2 weeks of planning and 3 hours to set up, including a further 2 hours to get the car on site at the bottom of a very steep incline. I wanted to give the car the mood of a 1960's shot but with a hint of danger, dare I almost say 'bond' feeling. The piece of work is entitled 'Escape to the Border' and hopefully almost has a feel of enemy border escape and darkest Russia to it.
Ambient Life - DCM Gallery
Ambient Life Web Site