This is just a ridiculous publicity stunt by Paddy Power. I'd hope it backfires on them, but then it will actually turn out better for them. Nobody outside of Manchester had ever heard of Fred Done before he famously paid out on Man Utd winning the title back in 1997/98 before Arsenal won the title. The free publicity from this stunt (and also limited risk - what Mancunian would ever place a bet on Arsenal to win the title?) went worldwide, now Fred has shops all over the UK plus a thriving website. The PR value of paying out twice far exceeds the cost of two liabilities.
Bookie pays out on United treble
I could understand them paying out on the title - a bold, but calculated move. Paying out on the two Cups as well is riding the publicity train as badly as those washed-up has-beens or never-wazs on the celebrity reality show circuit.