DENVER — For every five commercials Mitt Romney and his allies ran here in this vital swing state in the last two weeks of September, President Obama and Democrats ran seven, accusing Mr. Romney of having a “tough luck†attitude toward the middle class and asserting that Mr. Obama has brought the economy back from the brink.In Florida, the disparity was greater. The number of pro-Obama ads outnumbered pro-Romney ads by almost 50 percent — some 13,000 of them accusing Mr. Romney of outsourcing jobs to China, trying to gut Medicare and hiding his tax returns from the public.