>I can not agree with "every government has inherent tendency to get corrupted" for it puts the blame in an institution while corruption comes from within it's members, people. When you say that, it seems that other organizations, in particular private profitable ones, are immune to corruption, which is obviously not the case, as proved by current (and past) events (i.e. Enron, Mortgage Cos, Maddox, Siemens). So, as you believe that the government must be small to be less corrupt, do you think companies should also be small to get the corruption level low?

First of all, I applaud your principled response.
In regard to the source of the corruption, it comes from people, i.e. from inherent deficiencies of our nature. As long as any organization consists of people it is susceptible to corruption, i.e. it should answer your next question: it is not government only. Size of the organization is important because it helps to mask corruption. It is even more important, because bigger size means bigger power, and the latter is another efficient way to promote corruption, i.e. it assumes wider opportunities for corruption and less outside control.
In regard to private companies, I already answered that they are guilty too, but there is another line in this issue. We have anti-monopoly laws, and by good reasons. Why should not be the same reasoning applied to governments? Please, note that no corporation from your list ever reached the height of power and control assigned to modern, and not only modern, governments.