They always tell you to stop at the side of the run in ski school, but i totally 100% agree that boarders are the worst for deciding to take a break right dead centre in the middle of the run, but what makes it worse is that they do it in large groups. And especially in poor vis it makes a rather large obsticle for a skier, or fellow boarders for that matter.
But to put this into context, the skiers in question have probably had to swerve into a solid object such as a snow fence or piste basher to avoid colidong with and injuring the stationary boarders that were in the way. In the same way people often swerve into a tree to avoid hitting and killing a deer when driving. Its because skiers are just such good citizens.