Intel's Xeon 5000 series has risen in price over the past couple of years, but they also have offered a lot more performance from generation to generation. The high end consumer processors and Xeon 3000 series haven't changed much in their pricing since the introduction of Core 2. Roughly $300, $600, $1000+ tiers.
As to that affect on the Mac Pro? Well the $2,499 2006 Mac Pro used two $700 processors and the $2,799 08 model two $800 processors. The 09 DP model uses two $400 processors but cost $3,299. The $3,499 2010 model also will use two $400 processors. Make of that what you will, to me it says discount from the list price changed, Apple wanted much higher margins, or want to shift people to other systems that while offering better value for money make Apple more per sale. No because Intel have increased prices due to no real competition.