The month of May finds itself in a rather squishy spot this year, considering the release slates that have bookended it. April saw the blockbuster releases of Grand Theft Auto IV on the PlayStation 3 and Xbox 360, as well as Mario Kart Wii on Nintendo’s console, whereas June brings the promise of Metal Gear Solid 4 for the PS3, Ninja Gaiden 2 for the 360, and multiplatform efforts The Bourne Conspiracy, Lego Indiana Jones, and Guitar Hero: Aerosmith, to name a few.

By contrast, May’s highest-profile releases are Wii Fit, itself a game that has been subject to widespread shortages, and Haze for the PS3, which landed in critics’ laps with a resounding thud. Nevertheless, as evidenced by the NPD Group’s monthly sales-stat dump today, May easily maintained 2008’s double-digit gaming-industry growth, tallying $1.12 billion in total console, handheld, and accessory sales, a 37 percent year-over-year increase.

Unsurprisingly, April’s end-of-the-month releases notched three of the top five slots in this month’s chart, with the Xbox 360 version of GTAIV taking the top spot at 871,300 units. That tally is almost twice as much as the PS3 edition of the game, which occupied the fourth slot in NPD’s data charts with 442,900 units on the month. "GTAIV has now generated combined sales of 4.2 million units [in the US], making it the top-selling title of the year," commented NPD analyst Anita Frazier. According to Rockstar Games parent Take-Two Interactive, the game sold 8.5 million units and shipped 11 million units worldwide in its first 48 hours on the market.

Nintendo cleaned up the remainder of the top five. In the second slot was Mario Kart Wii, which added 787,400 units to the 1.12 million copies of the game sold in April. Wii Fit managed the third slot, coming in near the top end of analysts’ estimates at 687,700 units, despite the fact that many consumers have come up empty-handed when trying to buy the game at retail. Chart stalwart Wii Play, which comes bundled with a Wii Remote, rounded out Nintendo’s vice grip on the top five, logging another 294,600 units sold.

In the wake of GTAIV’s landmark debut in April, many were surprised that Xbox 360 and PS3 sales saw no corresponding bump; in fact, sales were down from the prior months. Although NPD analyst Anita Frazier said at the time that the uptick could be appropriately reflected in May sales (considering that the game was released so late in the reporting period), that has turned out to not be the case. For the month of May, the PlayStation 3 outsold the Xbox 360 by a growing margin, 208,700 units to 186,600.

As for those expected Xbox 360 and PS3 sales, Frazier has not yet given up on the prospect of a bump. "The continued success of GTAIV is not translating into big hardware sales for either the PS3 or the 360, but there may yet to be a lift in June due to gift-giving for Father’s Day and Graduations," commented the NPD analyst.

Otherwise, it’s the same old story for Nintendo and its fast-selling Wii and DS. Though nearly 50,000 units off of last month’s tally, the Wii still easily outpaced the competition once again, selling 675,100 units. Likewise, the Nintendo DS logged yet another 400,000-plus-unit month, selling 452,600 systems.

May 2008 has the dubious distinction of being the first month since 2000 where NPD has not submitted PlayStation 2 sales to the press. The omission is doubly strange, since last month the console was not far behind the Xbox 360 and its successor, the PlayStation 3.