Microsoft should be making a profit by now with the Xbox360, and if not, they will very soon. Sony's game division is still making money with PS2 and PSP sales. The Xbox360 will likely reach, and potentially surpass, the total sales of the original Xbox, and the PS3 will likely reach about those same numbers as well meaning that neither company will just call it quits just because Nintendo has so much more of a presence.
Nintendo's monolopy in the 80's came from the overly strict way in which they handled third party companies. Part of it can be forgiven because uncontrolled, unlicensed titles are what sped along the Crash of 83--but Nintendo took some measures that went a little too far--like controlling the cartridge supply and limiting how many games a publisher could make. Granted, a little more strict control NOW might be what the Wii could use to curb the influx of shovelware from worthless companies like Conspiracy and UFO.
Also, if those Apple patents are true, there could be a direct competitor to the Wii sooner than we might think. But, coming in so late in the game--even with a console of Xbo360-equivalent power that uses Wiimote-like controls--would likely not spell success for Apple. For the simple reason that they'd have less third party support than the other three companies, and they certainly wouldn't have the franchises that Nintendo has. However, I think I'd like to see another player enter the fray, if only to mix things up a bit. Every generation has had different players making consoles. I'd like that to continue. I'd hate for it to be "just" Nintendo, Sony, and Microsoft from here on out.