I think it's partly caused as you describe and also partly that they can afford to do things we don't have access to do. Just being "an accredited investor" means they can participate in IPOs and even now ICOs. This is where so much wealth is created. And then there is hedging in so many different ways that they are sure to always be growing wealth even if some things are declining. Buying multiple real estate properties, being able to develop raw land into income generating property, investing in multi-million dollar art, and so on.
So yes, there is some absolute corruption and exploitation going on, including "buying" politicians to make policy and tax law more and more favorable to them. But some of it is simply the cost of many of the things that earn the most.
Good points ;) They have the means to just make more because they have more, while those who have less are stuck just trying to just get by :/