Well I believe the idea is similar to what we have here. You...

Well I believe the idea is similar to what we have here. You load up your William hill card, you can use it at the bar, sports betting house, or online, so it's one account for everything, because as far as I'm aware in the UK you can't gamble physically with just a credit card, you need cash. Furthermore most sports betting websites won't let you withdraw your money onto a credit card. You'll need to wire the money which can take a few days. If you have a gambling card you can withdraw it right away, or use the funds to gamble at the pub without having to worry about taking it out of your online account again. It's simplification more than just convenience.
So people likely will use the credit card to put the funds into the site, but withdrawals will be more likely coming from use of the card. Physical gambling is common too, I go the the pub, I used to have a few drinks and gamble there with my mates (on occasion, I'm a little bit more frugal than they were.)
So yes it's still useful and going to generate revenue.