Nope. The 660 is a salvage part based on GK104.
GTX 680 (8 x SMX of 16 TMU's each with 12 shader cores - 8 SMX /128 TMU/ 1536 shaders). GTX 670 is the first salvage part -loses one shader cluster* ( so, 7 SMX /112 TMU/ 1344 shaders). GTX 660 Ti would be the second salvage part -loses two shader cluster (so, 6 SMX /96 TMU/ 1152 shaders)
I'm suggesting that either the GK104 has good functionality when it yields a serviceable die if Nvidia need a nine months or so (Q3 starts next month**) for a supply of second salvage parts. If there were a significant amount of GK104's coming off the line only partially functional, it would stand to reason that availability of 670 and 660Ti should have been the same as for the 680.
The other alternatives are that there are a supply of not fully functional GK104, but Nvidia is holding them back either to build up stock (unlikely), or because they have significant stock of GF114 (GTX 560) still to sell- it would also preserve their pricing structure. The third alternative- which I discounted is that Nvidia had built redundancy into the GPU -i.e. having an extra shader cluster built into the design (a ninth SMX for example) to allow for those GPU's that come out of the oven with a non-functional SMX to still be able to call on a full complement of shaders.
* SMX= Streaming Multiprocessor in Nvidia PR-speak
** The story says Q3 2012 and quotes Gibbo from OcUK who says "6 months" - that makes it October....October is Q4.