Showing passport at internet cafes

Does every internet cafe do it? I never found one that didn't. I heard that it has something to do with being able to track you down if you do anything illegal online. At one I heard a "Rich oil prince" scammer doing their work. Quite publicly, it must have been six booths down.

When you sign up to use any Internet cafe, yes, you are asked for some ID - being a local, I was asked to show my local driver�fs license.

Yes. Because the police department requests to do so.

If you are in the Tokyo area, there are a lot of places that have free WiFi. Places like FamilyMart, Jonathan's, train stations, etc... You don't have to show any ID to use those, though you may have to give an e-mail address.

In these days of free WiFi by many stores and restaurants, it's hard to say what a person truly needs an Internet cafe for, unless we are talking about a cheap place to sleep or bring a date (but don't get caught having too much fun), or self-indulge while reading manga.

If you are a foreigner traveling in Japan, you are supposed to have your passport with you at all times. Passport is the only valid form of identification for foreign travelers.

If you are a resident, show some other valid form of ID, I never carry my passport and couldn't show it if asked. If you are a visitor, then as mentioned you are required to carry your passport with you.
Among the reasons could easily be if you stay over-night (possible at many), then they would want to know who is on the premises - maybe to with lodging requirements.