That is also not correct.
GM204 GTX970, GTX980
The GTX 980 is the fully featured and working GM204 processor. All 4GB is available on the 256bit.
The GTX970 has 13/16 SM units, and has part of its memory bus re-routed, effectively still 256bit for up to 3.5GB, but requires an extra clock cycle to access the remaining .5GB. Drivers have taken care of most of the problem. You should not be purchasing the GTX970 or GTX980 if you expect to exceed 4GB of VRAM regularly anyway.
GM206 GTX950, GTX960
GTX960 is the fully featured processor for GM206, it is essentially 1/2 of a GTX980 in all aspects. Both 2GB and 4GB versions have full access to their memory through a 128bit bus. The GTX950 is 6/8 SM units, but still has a fully functional 128bit bus and access to all 2GB of memory (I don't think they make a 4GB version of this card)
GM200 GTX980Ti, Titan X
Titan X is the fully featured processor from GM200 offering 24/24 SM units and 12GB of memory through a 384bit bus. GTX980Ti is 22/24 SM units with 6GB of memory through a 384bit bus. It has full access to its memory.
What you don't see in the desktop lineup ends up in mobile. As an example the GTX980m is a GM204 with 12/16 SM units, so almost a GTX970 in a laptop.
So all the complaints are around a single GPU that performs exactly as it did before and after the realization that it isn't perfect. Which is something everyone knows when not buying a flagship product.