Possession is not ownership*.  The major exchanges hold a lot of coins but those coins (legally) belong to the depositors. This can't be reflected by looking at the address distribution.  Using the graph you used to illustrate a point would be like graphing where all the US dollars are and showing that 5 "people" (BofA, Citibank, etc) have 95% of the dollars.  Yes their is unequal wealth distribution in the US (and everywhere) but simply looking at who is currently "holding" the assets as a bailor is pointless.

* That being said if you don't have the private key for "your" bitcoins then you don't have any bitcoins.  At best you have an IOU for some bitcoins owed to you which hopefully will be paid on demand in the future.