The issue focused much of Monday at the Environmental Protection Agency's  headquarters in Washington DC.Why did President Barack Obama approve the Keystone XL pipeline?Keystone XL could boost US economyBy Glenn Kessler, BBC News, Washington DCUnder pressure from environmentalists and opponents of the pipeline, President Barack Obama approved the pipeline last week. Here are five reasons why it matters: Keystone XL would boost US economyPresident Obama says he approved the Keystone XL pipeline because it would boost US exports by cutting Canadian crude imports from the United States and