The other piece I left out earlier is that Apple rarely changes processors without a full model revision. Dell on the other hand is constantly looking at new processors and adding them as options, including cheaper Xeons at the same performance rating as older ones Apple may still be using.

In no way am I trying to say Apple is always price competitive. In my personal experience, again with USD, they are cheaper when comparing identical specs, when new models are launched. YMMV when the Apple model is dated, especially over a year old now. Or when comparing non identical specs. Apple does offer far fewer options from other vendors, resulting in situations where a similar spec machine may be available from another vendor.