Hinduism vs Buddhism

I remember when I first studied Buddhism and Hinduism in my sophomore year of High School. We talked about one of the major differences between the two was the idea of the caste system. In Hinduism you must perform tasks that will fulfill your caste your whole life and then when you die, you will be reborn into a higher caste. The only way to move up toward achieving Brahman is to stay within your caste and accomplish everything required of that caste.
One idea we came up with, is that this is a very good way to keep the status quo. Then the lower class people will feel no need to try to move up in society because they will believe that they must first fulfill this role and then next life they will be higher in social status. In Buddhism the belief is that anyone is able to achieve Brahman no matter where they are born into society. This way there is no status quo or caste system that you need to climb before you can be enlightened.
The caste system is an interesting belief when it is also thought that everything in the universe is made up of the same "stuff." Then why is there a system in which people are at different levels in the caste and are unequal.