The lighter the bike the higher the cost per pound. It's not difficult to do, it just takes money.

I haven't the chance yet to see Rob English's 10.8# bike, but when I lifted his 13# bike I was impressed. Light bikes are sooo fun!

As Andy noted, good quality frames are typically under 4 pounds. My latest frame is 3 1/4 pounds (minus paint). Add 11 1/2 pounds of components and whatcha got? Components are where the most weight is saved but also the highest cost. It's costs me about $300 for frame materials plus another $50 or so for consumables. Component cost? Don't wanna think about it!

As a point of reference I believe you can get one of Rob's superlights for about 12 grand. Given that you can't expect a $600 Jamis to be light.