its because intel wants its costumers to buy 1333MHZ FSB
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XPS M1730,IntelCore2Duo T9300@2.5GHZ,2x8800MGTX in SLI,4GB DDR2 667 RAM,DUAL 250GB 7200 RPM,VISTA HP with SP1,17" with 1920x1200 resolution
The E6600 is an older model. The E6x00 have been replaced with E6x50 which run on the faster 1333MHz bus. The new models are a bit faster stock but harder to overclock due to the already high stock FSB speed coming closer to motherboards' max FSBs.
If you want to talk about a CPU being expensive relative to its performance... go look up prices on Pentium 3s. Yes, they're still available for sale... typically in the $100 range.