[vladvasiliu]

I think this is highly dependent on how high-end the computer is or at least who their target user is.

My (old) MBP sounds great to me. My (much newer!) HP ProBook has hissing and various random noises when I move the mouse, and I can hear this even with cheap headphones tailored for conferencing. Don't know how "accurate" either one is, but no hissing wins for me every time.

I think you nail it with most decent motherboards. There are a lot of computers on the market, especially laptops, that are just cheap and try to get away with whatever low quality components and engineering they can. In particular, I'm thinking about HP "enterprise" models which are just awful. Their target audience doesn't really care about audio quality, so why would they? Most people don't have a choice when it comes to their work computers, so they may end up stuck with something mediocre. Then again, most people don't care, so there's probably not much hope to see any improvement on this front...