No, you are wrong. (this is fun)

http://en.wikipedia.org/wiki/Common_...ish_common_law

In 1154, Henry II became the first Plantagenet king. Among many achievements, Henry institutionalized common law by creating a unified system of law "common" to the country through incorporating and elevating local custom to the national, ending local control and peculiarities, eliminating arbitrary remedies and reinstating a jury system – citizens sworn on oath to investigate reliable criminal accusations and civil claims. The jury reached its verdict through evaluating common local knowledge, not necessarily through the presentation of evidence, a distinguishing factor from today's civil and criminal court systems.

I was slightly mistaken in that the King responsible for it, though he came after William I, was not a "Norman". Everything else I've said is true.

On the point of judges making law:

Judge-made common law operated as the primary source of law for several hundred years, before Parliament acquired legislative powers to create statutory law. It is important to understand that common law is the older and more traditional source of law, and legislative power is simply a layer applied on top of the older common law foundation. Since the 12th century, courts have had parallel and co-equal authority to make law[47] -- "legislating from the bench" is a traditional and essential function of courts¨