AFAIK, Hilton has it free in some countries and very expensive in another. For example, I know that Hilton SF (business district) has it free, but Hilton Prague charges you leg and arm...

Yes, it is true that many others have it free. This is true mainly in continental Europe. Very often, I have a feeling that the more expensive chain (not always better chain ) the more expensive add-ons are. Sometimes I think that they think like "if you can afford to stay with us, you can afford to pay for WiFi"...