Note that they aren't actually a courier company (let alone one of the largest in the UK, as claimed in one of the press releases), they are a reseller of other courier companies.
That is actually the easiest way to get BTC accepted, as you don't need the large companies to change anything, just the resellers.
Ah, that makes sense. If this is a success maybe individual companies will offer it as an option. There doesn't seem to be much of a risk for merchants if they use a payment processor so I can't see why not if it's still cheaper than paying credit card fees.
