Makers of video game consoles had hoped that the wild success of Grand Theft Auto IV, which hit stores in late April, would inspire consumers to buy hardware on which to play the game.

So far, that has not happened, according to the NPD Group, which tracks video game industry sales.

GTA IVThe research company late Thursday released its May retail sales figures. The top-selling game was (no surprise) Grand Theft Auto IV, which sold 871,000 units made for Microsoft’s Xbox 360 and 443,000 made for Sony’s PlayStation 3.

To date, said NPD, retail sales of Grand Theft Auto IV in the United States have been 4.2 million, though that figure excludes some retailers and it does not include international sales.

Big hardware sales have yet to follow. During May, Microsoft sold 187,000 Xbox 360s, while Sony sold 209,000 PS3s. By comparison, Nintendo sold more than the other two combined–675,000 units of its console, the Wii–even though there is not yet a Grand Theft Auto IV version for that console.

“The continued success of GTA IV is not translating into big hardware sales for the PS3 or the 360,” a NPD analyst Anita Frazier said. “But there may yet be a lift in June due to gift-giving for Father’s Day and graduations.”

(What could possibly be a more appropriate gift for either a father or new graduate than a video game console on which to fritter away the free time that comes with parenthood or entrance into the working world.)

More broadly, NPD said, the video game industry in the United States has generated $6.6 billion in sales this year – including hardware, software and accessories – putting it on track to achieve sales in 2008 of $21 billion to $23 billion.