What are the differences? Is it only the limitations like rows of data we can analyse and types of data sources in Public?
Currently, according to http://www.tableausoftware.com/products/digital#top-10-features-of-tableau-digital, two main differences are:
5. The ability to suppress underlying data
10. The ability to see and understand usage patterns
I am sure there are other differences, and I would recommend contacting firstname.lastname@example.org for more information.