Obama and Hitler had the power to make their words law, so that other people would kill foreigners in accord with their wishes/words/beliefs/etc.
Im not sure Id count that as a difference... All they did was give their opinion, and other people voted them into office because they were convinced by those opinions.
They arent responsible for their word being law - others are taking those words and making them law, be it the congressmen and senators who work the legislations or the people who vote for them and give them the power. The only real action
they take is to put their signature on things, which is still really only a formal custom to make sure the opinion given is real and correct.
When it comes down to it, democratic government is largely just a formalised method of people saying whose opinion they like the best and want to follow.
Osama had followers, a plan(s), and the ability to finance and execute them.
So, taking out the ones that are just words and opinions (gaining followers, having plans, and convincing the followers to execute the plans [unless Osama executed his plans himself... or did you mean he executed his followers?]), it seems like youre just left with money.