Part of that is true, but only part (trust me, I USED to work in the music industry). Mastering doesn't solely account for a clear sounding track. If the system outputting the mastered signal is CRAP, the song will also sound crap, and even if you use a good set of cans, it will sound pretty bad.
And then one more thing: no-one working in the music industry says eq is for DB's, cause EQ is the most important thing in ANY music production. Every production after the first sequencing stages, STARTS with EQ and ends with EQ in the mastering stages (mostly eq, and compression which is just a sophisticated way of eq-ing). But without EQ, you can't have a decent production, and you sure as heck can't have a decent mastering. So eq isn't for douchebags, rather for professionals.
And I mentioned I used the same headphones with the Lumia 710 and the 520...and the 710 sounds crap while the 520 sounds good, listening to the same mastered songs. So even with a good mastered track and a decent set of cans, if the system outputting the signal is crap, the track will sound crap.
Just to clarify for anyone not really understanding the "complete" signal-path being affected by the quality of the track, the headphones but also the system outputting the signal TO the headphones.
So I stand my ground in saying that the older 710 DOES need an eq.