Wrong.
Explosions are possible at any pressure with the proper oxygen to fuel ratio with an ignition source. Usually defined as LEL and UEL (Lower Explosion Limit and Upper Explosion Limit).
http://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html
In the mining industry, methane is constantly monitored. Any level above 1% and work must cease and the area be ventilated. The explosive range for methane is 5%-15%. Above 15%, methane will not 'explode' because there is not enough oxygen.
The explosive limits of gasoline is 1.4% to 7.6%. A much narrower span when compared to methane or many other flammable gases/liquids, but it can explode none the less in the proper circumstances.
Mythbusters disproved the exploding gas tank used so often in Hollywood scenes. For the most part, the gas tank has vapors are far above the explosive limit and once the vapors are exposed to the exterior they dilute very easily below the LEL. Hence the 'myth' was busted.