You are forgetting a namespace is a non-trivial matter and that it has scope implications. That is, this is not only a matter of preference. It needs to be weighted with the consequences. EDIT: and master5001 just named one example.It will tell you that the object is from the standard library. But since it is standard it kind of loses its usefullness.
You can't actually, because any name you define yourself outside of a namespace is not "standard". Consequently, when reading code the original programmer is making no distinction between his own names and those of the std.But even still, I can assume that whatever has no :: is standard.
Me the reader? Little probably. Depends on my knowledge of the language and how easily I can identify standard names at a glance and how much information I can retain while reading the code. Me the coder? Depends on several factors, but for the most part I can conceded to the fact it won't have any practical benefit in the short term.What will the std:: help you?
Question is if that is a reason to not write it. I tried to reason why it should be written on most circumstances. There's others I didn't find the need to repeat -- like Daved's call for consistency which is equally important.
However the strong point I try to make on that post is that we tend to look at readability as only a matter of form. It isn't. For me, the presence of std:: doesn't make the code less readable. It in fact makes it more readable. So there is also the issue as to exactly how many find std:: invasive.
Code readability on the other hand is much more about expressiveness, and while you can still make a case of std::, it will be a weaker one.