I agree. If the question really needs a country tag, but it is never provided or inferred yet is still a good question, answering "In the U.S. ...", or "In Australia ..." as a qualifier seems reasonable.
There's only so many options when the question is almost always from an anglophone (non-native speakers seem to be more aware of the need to specify ...
I agree, not all questions require a country tag. If a members requests one, and it's not needed we should point that out.
I also agree that mention of 401(k) is enough to say "US".
I do think that guessing is wrong. It might result in an answer that's incorrect-country-centric, only to have the OP add the correct tag.
Other than this, I've remarked ...
This is now somewhat possible. It wouldn't show for every single question, but we do have the ability to provide more just-in-time help based on the tags that people use when posting.
Can you give me some tags where it would be pretty important for them to specify a location within the question? I might be able to make quick work of this if so :)