It had to happen, sooner or later.

The first clue was Game Guy never finding an available Nintendo Wii in stock wherever he asked about them. A store here, a store there would receive maybe nine first thing in the morning, or early afternoon, and they’d be gone 30 minutes later.

The thing is, this has been happening almost since Wii debuted in late 2006 — one sellout after another. Even now, it’s not easy to clamp one’s grimy mitts on them.

Now, the market research firm NPD Group says those sellouts have amounted to something: Wii now reigns as the top-selling game console in the United States. About 660,000 Wiis were sold in June alone, pushing total U.S. sales near 11 million.

Micrsoft’s Xbox 360 was outselling all other consoles through Jan. 1, and passed the 10 million mark shortly afterward (It hit the market initially a full year before Wii). But Nintendo boosted productivity somewhat to meet demand and Wii began finishing ahead of both Xbox 360 and Sony’s PlayStation 3 in monthly and quarterly sales estimates as a result.

At E3 this week, however, you wouldn’t know there was a change in the new world gaming order. Each of the console manufacturers has insisted it owned the dominant device and promoted them correspondingly.

However, if Darwin — a prototype motion-sensitive controller said to work with both Xbox and PS3 — actually evolves, we shall see if Nintendo can continue shouting “Whee! over Wii sales.