No, it is not.
The Buyer Guide says "Buy only if you need it - Approaching the end of a cycle". This recommendation is based on the average time of release of refreshes of the MacBook Pro line, and not on actual facts.
The current 15" MacBook Pro with Retina Display sports the latest family of Intel processors (Ivy Bridge). In addition, it contains the top-range non-extreme mobile Ivy Bridge processors (i7 at 2.3 and 2.6 GHz, respectively, for the base and high end model). Intel has not yet released any processors that supersede or replace those found inside the 15" MacBook Pro. In addition, the 15" MacBook Pro is equipped with a NVIDIA GeForce GT 650, which is part of the most current famiy of NVIDIA mobile video cards.
So, there is nothing to update the 15" MacBook Pro with. It will probably get an update next year, though, when Intel releases Haswell, which is expected to arrive between March and June according to leaked roadmaps.