Originally Posted by
EuropeanPete
Isn’t the obvious answer here “why not”? If you’re asked for ID, a US driver licence is a form of ID and will generally be accepted unless you’re actually being asked for a passport. Few countries insist their hotels ask for what you describe as “legal ID” which is a concept which doesn’t generally exist: many countries insist locals carry ID and foreigners identify themselves with passports when asked at immigration and by selected security services, but that’s generally it.
As a rule of thumb, a driver license is not a form of identification outside the country of issuance (and the ocasional neighbouring or otherwise friendly country). In fact, in some countries it is not valid identification document even in the country of issuance (drivers are required to carry both the license and a national ID card). In Europe you may not board a plane or cross a land border (even within the Schengen Area) with a driver license (except for Nordic Council and Common Travel Area nationals). In most Asian countries you won’t be able to buy even a SIM card with a driver’s license.