Gamasutra pulled together a rough and ready numbers piece today, shunted from a substantial and detailed feature on Nintendo's sales, and ranked the Xbox 360, PS3, and Wii according to their software attach rates.
Any surprises? Just one. The PS3 had a third-party attach rate of less than two back in late 2006, just after it debuted, but Gamasutra's chart now has it nipping at the Xbox 360's heels with more than double that figure.
2.4 - Wii
1.4 - Xbox 360
0.9 - PlayStation 3
5.2 - Xbox 360
4.4 - PlayStation 3
3.1 - Wii
Gamasutra notes these figures are for the Xbox 360 after September 2007 and the PS3 and Wii after September 2008. If you look at the Xbox 360's life-to-date ratio, or 35 months, on the other hand, Microsoft's tie ratio rises to 8.1.
You have to be careful here -- high tie ratios are generally good, unless a system is trafficking unusually high numbers of units.
A console's tie ratio is equal to total software units divided by total hardware units. So say you sell 10 copies of 5 games for System A and System A sells 10 units, but you sell 10 copies of 5 games for System B and System B sells 50 units. The attach rates are going to be 5 (50 / 10) and 1 (50 / 50) respectively. System A has a much higher attach rate than System B, and so would appear to have the high ground, but System B sold just as many software units and five times as many hardware units, meaning that in this instance, System B is beating the snot out of System A.
Likewise, if you're selling very few hardware units, but lots and lots of software, your attach ratio is going to be high, while obviously failing to indicate your software platform's paltry sales, or give any indication what your install base looks like.
So who's winning? Hard to say. If you think install base matters most, then Nintendo, with some 16 million units sold in the U.S. versus 13 and 6 million for the Xbox 360 and PS3 respectively. If you think raw software sales trump all, Microsoft has around 126 million total in the U.S. versus 96 million for the Wii so far this year.
Several of you might further note that Wii Sports comes bundled with Nintendo's system (15.2 million copies), so you can't not buy it, and that Wii Play (15.9 million copies) is essentially free with the purchase of a Wii Remote. Either of these details may or may not skew figures, depending on your perspective.
Then again, if you just think "who's winning" is a dull, boring, last-gen game, hear hear, and I'll see you online to play something better tonight.