Because football has such a good track record of not squeezing every penny it can out of fans! (In fairness the £30 limit for away tickets is actually quite a reasonable measure).
Thin end of the wedge? In the first instance offer this great 40% off deal. The precedent is now set, games abroad are allowed. The next time it happens offer 10% off. The next time it happens offer a refund of just one game.