Mojang—creator of Minecraft—was thought to be outright boycotting E3 due to E3's main sponsor, ESA, supporting SOPA (Stop Online Piracy Act). Carl Manneh, the "boss" of Mojang, was quoted as saying, "The organization behind the convention supports the SOPA initiative in the US. We are against it, and have no wish to support those who support SOPA, it's as simple as that. So we're not going."
Kotaku pressed the matter further with Manneh, and he explained that they aren't exactly boycotting E3; they just aren't going. "We are just not attending," he told Kotaku. "We didn't have any specific plans for E3 (whether or not to go), but when we found out that ESA supported SOPA, we decided not to go."
It sounds like a boycott, but that's making it way more dramatic than it really is. Then again, what would the Internet be without making mountains out of molehills?