03-11-10: Almarg
And of course the computer speakers don't have any deep bass, which is a major cost driver in a quality system.
Another factor is that the speakers, sound card, and heavily processed source material probably homogenize the sound, making mediocre source material sound more pleasant than it would on a high quality, more revealing system, but sacrificing the ability to make high quality material sound as good as it should.
By the way Almarg the speakers aren't computer speakers. They are the Philips mini system speakers and produce some fairly prodigious bass which is what attracted me to this system in the first place. Of course these speakers can't do reference levels, but bass is one of their strong suits.