Softpedia points to a Nvidia Developer Zone forum post revealing that the company has removed a specific Linux feature as of the v310 drivers due to the Windows platform. A BaseMosaic user on Ubuntu 12.04 noticed a change in the number of displays that can be used simultaneously after upgrading from the v295 drivers to v310.
According to the post, the Ubuntu user connected three displays using BaseMosaic, backed by Nvidia's v310 drivers and two GeForce GTX 560 Ti cards in SLI. But after configuring the xorg.conf file and adding the supposedly supported fourth display, only three monitors would light up.
Source and more: Devtalk.nvidia.com via Toms Hardware
I don't really know how reliable the source is given that we don't know who forum user "sandipt" is, but if this is true, what the actual hell? If they want "Feature Parity" between operating systems, why is Linux getting quad monitor support removed, but Windows gets to keep its Optimus support?