Spring RTS Engine

Exactly! Anyone who feels that music must be heard most clearly already has a pair of high quality headphones/earbuds, and anyone that doesn't care about the highest quality can buy a replacement set for less than $5. Why mention $5 earphones on a review for a $300 music player?

That's like saying, "Well the new 2008 Ford Four-Hundred is a beauty of a car with superb performance, sporty design, and great suspension, but the Ford logo on the back isn't the shade of pink I like, so I'm deducting 10 points. In summary go for the new Volkswagen Queershlughkenfurten. It doesn't come with designer extras like wheels, but the logo is top-notch."

decent quality headphones are worth more than 5€...

your example doesn't fit; it's more like mounting truck wheels on a spors car, what kind of performance you'd expect?

said that, it's not that audio quality is really that absolutely important when it's about mobile players, the fact itself they do use mp3 or any lossy codec makes the quality quite poor, you use them while walking or while travelling in a train where teh background noise it usually high enought to not let you hear the fine details.
You can hear differences to lossless encoding (even a portable cd player) when you link them to a serious hi-fi system.

the last word, hell you pay 300+€ for this/those player(s), you'd expect it to be good in all it's parts, not to have to replace (and spend more) some components right after you bought it to be able to use it's full potential.