For the reasons listed earlier and also the fact that the republicans are really hated over here especially for the Iraq war which was a horribly reckless foreign policy decision that destabilized the middle East. A lot of it is a reaction to the fact that Obama was seemingly the exact opposite of Bush to us he appears far more intelligent more charismatic less gung ho has more dignity but here are other reasons.

He believes that global warming exists and is man made and has taken some decent measures to protect against the impact of global warming, he's been far less hawkish militarily and has reopened diplomatic relations with Cuba which will help bring down communist leadership there, he has worked with the international community to ensure that a deal is in place that will stop the Iranians from getting a nuclear weapon without resorting to a reckless and dangerous war. He ordered a successful and bold operation that killed Osama Bin Laden. He turned around and made his economy far more stable than most leaders in Europe after the worldwide economic recession. He helped breed a culture that mostly accepts rights for homosexuals. He stopped many of the torture practices Bush placed that acted as a propaganda tool for radical terrorists and he has stood up to AIPAC and the war mongering Netanyahu more than any other president before him. He has successfully economically isolated Russia with the help of the international community, he has helped set in motion the process that will eventually modernize healthcare in America. The successes go on, he's made some huge blunders in Libya and Syria but his track record is far more impressive than his predecessor.

JFK is popular here because he was a charismatic Catholic with Irish roots and I think Clinton is popular because of the work he did in helping simmer down tensions in Northern Ireland although I myself am not a big fan of either of those presidents.