It all depends on what the customer is going for.
For my hosting business, I have an option to go with an IDE drive and a Celeron processor. However, since I want solid hardware supporting my shared-hosting clients, many of whom are fond of CPU-hungry applications, I will bite the bullet and pay extra for the SCSI drive and the Xeon processor.
For some of my clients who are starting to outgrow the normal shared-hosting environment and just need gobs of space, the SCSI / P4 configuration works just fine. I like the performance of the Xeon better, but if I'm potentially going to be profiting less from the boxes *and* the boxes are going to be storage depots, I'm willing to drop a step in processor-power and provide the clients with a lower-cost option.
Now I just have to hope that that policy doesn't come back to bite me on the backside