HT_Black said:
It's definitely intentional, like how violinists will make their E string slightly flat when playing in minor key. In this case, it makes the song sound dead and echo-y, pardon the Buffy speak.
I agree that it's intentional to make everything sound more bleak.
What you said about violinists playing their E-string flat though is not true. Unless it's a very specific case, in general, you play your instrument fully in tune.
A key becomes 'minor' when your 3rd note in the scale is played half a semitone flat, and then there are variations on the 6th and 7th notes depending on the variation of scale (such as melodic or harmonic minor scales).
If you are thinking of violinists who play at a virtuoso level, then you are probably thinking of "expressive intonation". But all that is, is a slight exaggeration of the notes to enhance the effect of a particular sequence.
The strings are still tuned in perfect 5ths -- unless a conductor or group purposely decides beforehand which is extremely rare, even in modern cases.
Just because something is flat, doesn't mean it's minor.
Also just to clarify, there is no perfect system for temperament, every system has to compromise, but tuning strings to perfect 5ths is the best general method. Since your E and G will never be played simultaneously, it's not a big deal that they are not in tune technically together. In segments that require full chords of 3 or even 4 notes, your fingers need to take this into account.