With Nintendo announcing its global software tie ratio (attach rate) this morning, we were curious to know what the current software sales ratio was in the States for current-gen consoles. We contacted NPD, which gave us its latest figures. The data represents the amount of software sold per console divided by the number of consoles sold in the US.

• Xbox 360: software sales ratio: 7.5
• Wii: software sales ratio: 5.3
• PS3: software sales ratio: 4.6

Just for kicks, we asked about the Nintendo DS and Sony PSP, which have the ratios of 4.7 and 4.2 respectively. The data shows a significant change since the last time we checked in half a year ago. The Xbox 360 has maintained its solid lead, but the Wii has rallied from 3.4 to 5.3. As always, we do have to take "software" top-seller Wii Play skewing the data into account, but Super Smash Bros. Brawl and Guitar Hero III also helped. The PS3 has ticked up one game from 3.5 to 4.6. The real takeaway from this data is that console owners are growing their software library no matter which console they own.

Despite consistently strong hardware sales, the Wii has thus far lagged behind its competitors when it comes to the all important software tie ratio. The New York Times looked into the problem today, with an article highlighting Wii owners' reluctance to buy games at the usual rapid pace.

On average, Wii owners only buy 3.7 games a year, compared to 4.7 and 4.6 for the Xbox 360 and PS3 respectively. "These new gamers are content with the games they have, often going no further than the Wii Sports game that comes with the machine," the Times author states. "They don't buy new games with the fervor of a traditional gamer who is constantly seeking new stimulation."

Analysts say fixing the problem will require changing the way third parties market their games to the new audience of casual Wii gamers. "Advertising on Game Informer and 1up.com just isn't reaching this audience," Wedbush Morgan's Michael Pachter said. Advertising on Joystiq.com, though? Always a great idea!

Ben Schachter, analyst at UBS, tells investors that they shouldn't judge Grand Theft Auto IV's success on total sales, but on the game's tie ratio. What Schachter means is that GTA IV's success can't be compared to previous GTA's raw sales numbers because there just aren't as many now-gen consoles in homes as there are (were) PS2s and Xboxen. He believes the game must be measured by the number of units sold divided by the number of consoles available to play it in consumer's homes.

Schachter postulates that if GTA IV receives a Metacritic score above 95 that the tie ratio could hover around 30% of the available market, meaning US sales could eventually reach between 7-8 million units. He believes globally that sales could reach 10.5 million units by the end of this year. Schachter concludes that GTA IV sales will meet or exceed expectations but the strong sales won't protect Take-Two from the grasp of Cthulhu EA.

The Nintendo Wii saw a surge in game sales in December, with NPD Group reporting (via IGN) the software to hardware tie ratio for console reached reaching 8.11 for the month. That means approximately eight games were sold for every Wii console sold during the month. Top software sales for Wii in December include Mario Galaxy (1.4 million), Wii Play (1.08 million) and Mario and Sonic at the Olympic Games (633,000).

It should be noted that the 8.11 statistic doesn't reflect the overall tie ratio -- if 7 people who already owned a Wii bought Mario Galaxy and an eighth person bought Galaxy and a Wii, the figure still holds -- but it does boost the console's life-to-date tie ratio, now resting at 4.64.

The tie ratio for PlayStation 3 was 5.04 in December and 4.24 life-to-date, while the Xbox 360, with one year ahead of its predecessors, still holds the dominant position with 7.76 in December and 7.0 overall.