not true. Windows will support up to 9 monitors. And nVidia cards will support up to 2 monitors per card (with the exception of the upper end cards which will do 3 each). The limit of 3 monitors only applies if you are linking the cards (SLi), otherwise they are treated as 2 stand-alone cards in windows and you can do 4 independent monitors.
Actually you can use as many as you have dvi ports. You can even use surround gaming by using a program called softTH. Its free and works by making one graphics card do all the processing and any other outputs just act as the outputs making it so that you can use all the monitors all the way up to 255 with this program.