The Wii's US$249 base price always allowed it to be known as both the cheapest console and the best deal in town for next-gen gaming. Even at a price of US$60 a pop for the WiiMote and Nunchuk, the cumulative price of the system and four controllers would still be under the cumulative price for the Xbox 360 and PS3. This all changes with the Wii MotionPlus.
Part of the reason why we're comparing four players is because of the way Nintendo sets up its games. While it's very rare for Xbox 360 and PS3 owners to have four controllers—partially because their online connectivity is so good—it's very common for Wii owners to have four. You need four controllers to play four-player Wii Sports Tennis. You need four controllers to play Super Smash Bros. Brawl. You need four controllers to play Mario Kart Wii. It's very much a living room system, something that's emphasised by Nintendo themselves in their own advertising.
And what do we find when we compare the Wii with four controllers to the other systems with four controllers? That the Wii is US$20 more expensive than the Xbox 360, and only US$10 cheaper than the PS3. That's definitely NOT the cheapest console.
In the interest of fairness, we compared all of Nintendo's accessories (the Wheel, the Zapper, Retro Controller, Nunchuck and Balance Board), and grabbed the cheapest one's price point—the wheel at $14. We priced the MotionPlus at the same price. So far Nintendo has only said that their Wii Sports Resort will cost $49, with one MotionPlus accessory, but nothing about how much the accessory will cost on its own.
It's also necessary to note that if you buy your first MotionPlus the smart way, with Wii Sports Resort, you'll have to pay $35 more than the price we calculated with buying only the accessories. This pushes the Wii into the "most expensive console" territory at US$525—which is above even the PS3.
We also didn't include those other accessories like the wheel or the zapper as a "necessary purchase" because they're not necessary to play all games, and are only directed toward a certain title niche. The MotionPlus, on the other hand, is a necessary purchase to play a big chunk of upcoming Wii games, since many games starting from the next year on will require the MotionPlus as a necessary accessory to enable accurate motion detection. As Mark said in his hands-on impressions, the MotionPlus is so good that gameplay without it feels incomplete. Nintendo has gone back and retroactively made your current experience (in relative comparison) worse by introducing this new accessory. Do we think Nintendo is right in releasing this accessory? Of course. But by doing so, they push themselves out of the cheapest console throne.