I'm afraid that's right.
It's not always right, though; the good news is that increasingly, hotspot operators are getting together. So my favourite hotspot operator - Broadreach - runs ReadyToSurf and that's available through Virgin and BT Openworld - and others. But also, some other big hotspot operators will let you log on if you have a subscription to their networks, at ReadyToSurf.
If you have a ReadyToSurf account, you can actually get billed for your online time through your broadband supplier, per minute, and you can log on through a great many hotspot locations. As time goes by, I expect you'll have a lot of trouble knowing, for sure, which operator actually owns the hotspot you're at. The hotspot may recognise you from a "cookie" on your PC...
ReadyToSurf is a good place to look!
But quite a lot of hotspots are actually free. So it's worth exploring...
Cheers,
Guy