The difference is that corporations have (mostly) voluntary membership but unelected leadership, whereas nations have (mostly) involuntary membership and elected leadership. So it still stands that it should not be the expected state of affairs that corporations are seen as stewards of the common good, rather than the government. It really ought to be the other way around, and the fact that it isn't is sign of a problem.
I don't remember who said it, but there is a quote along the lines of: "People should look to the private sector for growth, and to the government for justice. Increasingly, they look to the government for growth and to the private sector for justice."
Edit: Found proper quote and source thanks to mbrock's pointing out where I likely heard it last.
The quote is:
"We have come to rely upon capitalism for justice and the government for economic stimulation, precisely the opposite of what reason would suggest." - Donald Kaul
And it comes from here: http://articles.philly.com/1990-10-17/news/25891604_1_budget... (Timothy Taylor did quote Kaul in the podcast mentioned in the comment below)