I used to think that but not everyone's EQ is made the same. The EQ in wmplayer is god awful. I've tried it and of the 4 headphones I've used it on, the sound is better with it off because it doesn't really gradient the sound spectrum well. I'm sure with a good hardware EQ, this could be true but then, I'm figditing with the EQ for every different genre of music... that is the definition of not fun.
Flat sound sigs are good for those that like that, and are great for those that actually record for a living but for people who just like a good quality sound coming out of their player, and don't want to hassle with a poor software EQ, flat falls, well flat.