is that you will not be covered by the manufacturer's warranty terms if the machine is exported from the UK.
Otherwise I can see only one reason why a maker would not want to ship a machine to you. Shipping computers does carry an inherent risk of damage, and you may have to agree to an "own risk" clause in the terms of sale. It obviously wouldn't be a viable proposition for a manufacturer to accept liability for damage caused in transit - it wouldn't be worth the cost of shipping the computer to and from the UK for repair.
There's also the fact that the cost of shipping would have to be added to the price.
I have a client in Sydney who tells me that he has no problem getting good spec machines - would it not make more sense to ship from there?