Nigel - yes, during manufacture thread is twisted one way. If you run a length of thread between finger and thumb you can feel it's smoother one way than the other. Sewing against the twist leads to tangling and knotting, sewing with the twist is easier.

As one who has spent many an hour with needle and thread I know whereof I speak.

Threading is also helped by cutting a diagonal 'point' on the thread with fine sharp scissors first, not as difficult as it sounds!