Things may have improved recently in the UK, but a couple of years ago it wasn't unheard of for hosting companies to charge significant release fees for domain transfers, and to delay transfers for weeks or months - sometimes for so long the national registrar had to get involved.

Another popular scam was to lock access to an account when a charging period expired so the owner couldn't access any domain transfer tools, and only allow access and transfers on payment of another full year of hosting.

It's a shady business. IMO there's no real reason why it should be.