See, I thought it had to do with the fact that VFR aircraft operate under 10,000 ft., and usually below 250kts, so it was set to 250kts for safety reasons in that regard, and well as the fact that under 10k is generally more populated than higher altitudes.
Here's my suggestion.. don't worry too much about what it's like flying in the real world. Most of us are stuck in the pretend world, and so we should live with within those parameters. Considering jets like the MD11 typically clear 10,000 w/in 5 minutes no matter what the speed, who cares? Plus, if you're following your SIDS/STARS like good little boys and girls, then you need the maneuverability of the lower speeds to accommodate those flight paths.