My take... Historically there are specialists for data such as Business Intelligence, Network Architecture, ETL, etc. They know how to move, manage and scale data.
Then there are the analysts that use the data such as Statisticians, Engineers, Physicists, etc. This is more the applied side of data.
The advent of computing power and speed of networks has allowed data to be more accessible. Now there is a need to merge these two specialities together. The Data Scientist knows enough of ETL and knows enough of applied math and statistics. This may be more of a generalist role.
