The lower bound that we did for sorting was very specific.  It was
for sorting in a comparison-based model, and it worked for any data
types with a compareTo.

Radix Sort is not comparison-based, and only works on certain types
of data.  Also, while Radix Sort can be made linear for most realistic 
scenarios, it is important to note that if the data is extremely sparse
across its range, Radix Sort is not actually linear.