Actually, Pwn2Own doesn’t include Opera because they argue that it is too insignificant. Being one of the +220 million insignificant users of Opera, I would like to let Pwn2Own hear my voice: “Include Opera next time!”
It may be closer to bulletproof than other browsers, but it is unfair to Opera to exclude it thereby letting potential vulnerabilities remain undiscovered. All other major browser competitors are included in the contest, consequently gaining an unfair advantage.