Lu
"I believe the difference covers the shipping from the USA"
US - $139.95 and UK - £139.95
Do the math.
Our British friends are being charged $256 (£139.95) for something which costs $139.95 (max) in America.
Even if they had to pay their Value Tax and shipping, they could still buy it on the net for less than a £100, a saving of £39.95 on the British price.
If they get the 15% discount you said, it would cost them less than £90.
If they buy on a visit to America, the same product will cost them only £76 - not much more than half the UK price.
Or £65 if they get 15% discount which is less than half what they'd pay in England