Why have region 2 for DVD players and region b for Blu-ray players?

DVDs are coded into one of five regions (1 - 5)depending on where they are sold around the world. Blu-ray discs on the other hand are divided into three regions (a, b, c). The regions are purely commercial and are used to prevent content intended for one market being sold or used in another. Licensing agreements between publishers and rights holders mean there are different restrictions for HD content.

There is no technical reason for the difference in region coding nor for the use of the coding at all.