In Linux, you are using Intel on most computers where the BIOS is set to use hybrid. (If you install the NVidia proprietary on such a laptop, Intel's 3D gets disabled)
Many BIOS'es have an NVidia/ATI only / Win XP mode option, which lets you use the NVidia / ATI always. And within a year I expect it to be possible, to run a specific program on NVidia (don't know about ATI) when starting it with a special command. Automatic switching is not yet working, but we might get that with Wayland within some years.
That second link of Lynden, is Bumblebee 3.0, which was announced on phoronix some time ago. Since version 3.0, it automatically powers down the unused GPU. It's probably the hybrid graphics switching tool for Linux out there, at least if you have nvidia Optimus and not AMD.
Getting nVidia only laptops (which I think is what you mean by "discrete nvidia" is hard nowadays. Hybrid nVidia+nVidia setups don't exist anymore in today's laptops, and nVidia only is also becoming very rare except for laptops that have Linux preinstalled.