Very good question. It is factually the case that the Nazi's drew their support from the middle classes. The Nazi party became the biggest party but the two working class parties together, the SPD and the Communist Party where bigger combined.
So why did middle class people tend to support the Nazi's, well I guess it was because of a number of reasons. Firstly the economic crisis meant that the living standards of the middle class was falling, those who were middle class were going to become working class. Whatever the case many of them were heading for a life of poverty,
Secondly, because of this fact middle class people lost faith in their traditional conservative parties, a political vacuum was formed, which was either going to be filled by the left of the right.
Thirdly, the middle class hated big business, they hated the banks and bankers etc, the same as the working class did, but they were more open to arguments that those below them, workers, particularly workers organizations like unions, immigrants, minorities and Jews were equally if not more responsible for the economic crisis that they were suffering from.
The reason the working class didn't tend to support the Nazi's was because they had more effective and collective means of resisting the ruling class, unions to launch strikes, established political parties, like the SPD and the Communist party, working man clubs etc etc. The middle class, small shop keepers, farmers and small businesses don't have this collective nature, nor did they have the traditions of the working class.
However it is the case that the Nazis got support from big businesses and corporations because they saw them as a way of subduing strikes and an unruly working class. In the 1930's the combination of a dissatisfied middle class, a worried ruling class who wanted someone to suppress the working class and lots of brutalized war veterans to provide street fighters meant that the Nazi's now had an audience for their racist fantasies, a movement on the streets and material support. Though they didn't come to power unopposed. It could all happen again.
