When you go portable you wind up sacrificing processing power. Laptop CPUs are generally clocked lower to save power, allowing for a longer battery life and to reduce heat. The laptop form factor does not allow for very good heatsinks on the CPUs so you can't clock them as high as a desktop without running the risk of overheating, especially with the quad core CPUs. The quads also use a lot more power than dual cores so clocking the quads as high as the dual cores would cause a significantly shorter battery life.