“Who said mobile gaming has to be casual?” quipped Google’s engineering director, Chris Yerga, at the company’s launch of its first ever tablet this morning. I wouldn’t go quite that far, but the 7-inch (1280 x 800) handheld does have attractive mobile gaming specs: a quad-core Tegra 3 CPU, gyroscope, accelerometer, and a 12-core graphics chip. At $249 in Australia next month, can you see yourself on the train with one instead of, say, a ~$349 PS Vita? Watch the Nexus 7 in action…