I suspect the reason that they did this quietly was that these are not new Mac Pros at all. Rather, they are same as the "Mid 2010" models they replaced, with minor bumps to the CPUs and memory. They continue to use the same generation CPUs that were available in 2010 (and same chipset, I presume), despite the fact that newer generation Sandy Bridge CPUs have been available for months now.
IMHO, the RAM bump wasn't even that good -- the base config now includes only 6GB, which is still laughable for a professional machine costing $2500.
The CPU offered in the lowest Mac Pro today is the W3565, a "Bloomfield" model, based on Nehalim-B. For the record, that is now three generations behind, being behind the W36XX "Westmere"/Nehalim-C Xeon chips, the Sandy Bridge Xeon E3/E5, and the Ivy Bridge Xeon E3. A quick Googling cannot give me when the Ivy Bridge E5s are due out, but probably not soon.
EDIT: Apple does offer "Westmere" Xeons, but only as 6-core CPUs, which when looking at the website, is all but the cheapest option.
I remember in 2010 writing about how it was quite possibly the worst time to buy a Macbook Pro because they don't change the price even though the hardware was extremely old[1]. Then I did a followup story[2] when they updated the hardware and the internals were still not up to par for comparable machines.
I always thought it odd that they don't discount their outdated machines. Buying a MacBook Pro last week was a raw deal. Apple sells hardware that is two years old at higher-than-competing-modern-machine prices, but people buy them, so they must be "good enough" or enjoyable in some other aspect.
IMHO, the RAM bump wasn't even that good -- the base config now includes only 6GB, which is still laughable for a professional machine costing $2500.
Pretty pathetic if you ask me.