We discussed that, but we decided against it because 1) it might be confusing (and the directed vs. undirected degree issue is already confusing); and 2) you can add the column yourself if you need it.
To add a Total Degree Centrality column, do this:
1. Add a new column to the Vertices worksheet.
2. Format the column as General, not Text.
3. Insert this formula into the new column's first data cell. Excel will automatically copy the formula to the entire column.
=SUM(Vertices[[#This Row],[In-Degree]]+Vertices[[#This Row],[Out-Degree]])
4. Use NodeXL, Analysis, Graph Metrics to calculate In-Degree and Out-Degree. The sum of the two will appear in your new column.