I believe we can't misunderstand greed with ambition. I think @redsun114 meant ambition by his example, because that is what lead us to seek for more money, for better life quality, for status and every other human needs that for some seem bullshit, but for others are necessary for their personal fulfillment and happiness.
Greed, on the other hand, is the insatiable characteristic some people have inside themselves. In this case nothing is enough for the person. He can have all the money of the world, best life standards and status on his society, but he still want more, even though it's not possible. These people losing all their money trading and gambling due to greed would act in the same manner if they were in a superior position, and some of them were for a while and lost everything for being insatiable!
Great that you break it down in order for them to clear out what they are talking about. So, according to your explanation, we can clearly see that ambition is much better than greed but too much ambition can occur too for us humans and this doesn't differ anymore from being greedy.
Speaking of greedy, many of us are currently suffering from it even though we know that it's wrong. In life, we should have this so-called contentment so that we won't fail if we are already at the highest peak of our careers. A lot of poor have this trait already but I think they need to try harder because they are still at the lowest point of their lives.