In any case, MSAA performance is a moot point in modern games thanks to deferred rendering, thanks to consoles.
CONSOLES STOLE OUR MSAA!!!
That is not the reason for deferred rendering
Here is a very small account about forward and deferred rendering http://www.anandtech.com/show/5458/the-radeon-hd-7970-reprise-pcie-bandwidth-overclocking-and-msaa/3 and they do mention the memory constraints of MSAA on deferred rendering.
They also talk about Forward Plus rendering, proposed by AMD and used at least on the Forza series on the xb1.