It IS normal. The only way you can keep your little guy from being bit by other one and two year olds is to keep him away from them.
MY son was the biter (probably some moms lighting up the mommy blogs about him this time two years ago). Biters can be supervised, given consequences, given other strategies - but until they mature, and learn more self control and social skills - they will bite. Even though my son KNEW it was wrong, he could not stop himself because he did not have the self control.
Kids are more likely to be bitten during transition times - so the teacher always shadowed my son during those times.
On a positive note, "Whats the worst that can happen?" Both of my children have been in daycare and been bitten repeatedly and are none the worse for wear. Every once in a while - a little mark or bruise results from it.
Also - use this as an opportunity to teach your son to stand up for himself - look the biter right in the face and say strongly "No. I don't like that. Biting hurts. Don't bite me."
You must be wrong on the numbers. The legal ratio is 1 to 6. If its 1: 12 your school is breaking the law.