It looks like different testing stations have different rules. Merv has had the same problem with regards the grill.
I was a bit surprised at the tyre aspect issue especially when my brother in law has an HSV with different aspect tyres front and back as standard straight out of the factory. The testiing station seems to think that tyres of very slighlty different aspect is less preferable than tyres of differnt tread/manufacture front and back.
Anyway I will need a new set of rears in the future and the grill will have to be removeable
in order to clean out the flies etc.. as will the exhaust covers.