Okay firstly, sorry to necro a year old thread with no replies...
Secondly, the 8x8 doesn't refer to the number of wheels that are steered. It refers to the number of wheels that are driven. The first number indicates the number of wheels on the vehicle by the number of driven wheels... so nothing would ever be called a 4x8 as that would be saying that the vehicle has 4 wheels and 8 of them are powered... it would be an 8x4, but in this case, it is still an 8x8 as all 8 wheels are powered.