In case of physical presence it's possible not to ask for an ID if a person is clearly looking like an adult.. Perhaps something similar could be implemented online.
I don't think it's fair to ask people for ID when there is no suspicion of violations.
The problem is that an online user can't be suspicious, the operators can't see him. The operators only see a nickname and an email address. The only thing they can do is request verification which can still be cheated but most people will not go through the trouble of submitting someone else's personal details to be able to gamble.