Josh Roberts got his first video game system — Atari — when he was 4, and since then, “I’ve had all the latest and greatest systems,” said Mr. Roberts, 27, an advertising account executive. The roster includes various versions of Nintendo, Sega and Sony PlayStation, the original Microsoft Xbox and now its latest iteration, Xbox 360. Last year when Mr. Roberts moved with his wife from Los Angeles to Memphis, he didn’t have cable for several months. So he began using his Xbox 360 for something more than his standard fare of games like Guitar Hero II and Madden NFL: he downloaded episodes of his beloved “South Park” as well as the occasional movie in high definition, for fees running from $2 to $6 through