Yes you are right, steemit is actually not decentralised. It is in fact a company registered in NY. So that is an avenue of attack, however the blockchain itself is decentralised. It's on computers all around the world and even if China, Russia and the US got together to unplug all of those computers steem would continue.

I don't know of a portal into the steem bc (busy/steemit/zappl and many more) that is not decentralised. However, with not too much technical skill we can all build our own portal in. It won't be as polished as the above but the functionality is there for all of us and that cannot easily be taken away.

The whales, whilst they have a lot of power, are not centralisation. They are points with a large amount of power but they cannot dictate what you do or write. All they can do is make it harder to find you. Youtube and FB on the other hand can literally stop your content. BTW technically steemit/busy etc can also can also dictate what you see however that would not last long at all.

Governments and corporations are single entities. Each whale is for the most part a different entity with their own ideas and ways of thinking. They might come together on issues but it's not the same as a government or corporation.

Thing is, the whales have to be careful because if they are irresponsible they risk losing everything overnight. That's millions of dollars they can blow if they are too douchie. So it behooves them to take right action. And if one or two whales jeopardise the system it is definitely in the interest of the other whales to correct that. This is one of the philosophies behind steem's voting system and is covered in the white paper.