Do you think the Protestant Reformation succeeded in large part particularly because of the political ramifications of the break from Rome? I imagine that such a break would have been somewhat attractive toward nations looking for greater autonomy in their internal (and external) affairs, and the fact that Luther was protected by Frederick (Frederick III, I believe) in northern Germany testifies to this. I would imagine that such a radical theological break would not have been quite as attractive to the peasants as it would have been to the ruling classes, particularly those that were far from Rome. Henry VIII's desire for autonomy in England and break from Rome reinforces this possibility that I am suggesting.
Actually I would argue that the peasants found the Reformation appealing because Protestantism championed their cause by insisting the Bible be translated into their local dialects. Protestantism inherently became a bottom up movement rather than top down. Having secular rulers jump on board accelerated the process and served to legitimize the movement as a whole.
Why did Luther side with the nobles' attack against the peasants who didn't go along with his views? I'm referring to the Peasants' War of 1524/1525. That seems to suggest that it wasn't necessarily a peasant phenomena. Also, his appeal to Frederick III in 1521 seems to have preceded his translation of the Bible into German (1522). When you refer to a “bottom up movement” do you mean in general (e.g. after Luther's lifetime)? That might be true.I think that during Luther's life, the people who probably welcomed his dissent were rulers who wanted to leave the authority of Rome, and also reformers/scholars who seemed to be growing in number toward the late Renaissance (Erasmus, Thomas More, and others) anyway...the people who were vocal about abuses by Catholics, particularly in regard to indulgences.
I was considering Calvin, Zwingli, Knox, Tyndale in this question and not just Luther alone. Luther obviously had to have time to get the Bible written into German and he needed a patron for this to happen. Thus he secured his patronage first through Frederick. Luther was a headstrong jerk too when it came to somebody disagreeing with his views. It doesn't surprise me that he moved to crush the peasants who dissented against him. But on the whole, the Reformation happened because there was an outcry by the common man to have greater access to his religion. All the while, secular rulers exploited the cause to suit their own political ambitions, and at the same time, pacify their people.