I think you are quibbling with semantics.

In terms of SQL Server Backups, I was under the impression that the term "Differential" is synonymous with "Incremental".  If you look at your choices in EM, you can choose Complete or Differential, as oppposed, say, to a Full-Text Index, where you can do Full Populations or Incremental Populations.  The Micro$oft team simply wasn't consistent with their terminology. 

The Differential truncates the Transaction Log.