I was re-reading The Elements of Style when I noticed a remark I had previously overlooked in the third rule of usage (Enclose parenthetic expressions between commas.).
The abbreviations etc., i.e., and e.g., the abbreviations for academic degrees, and titles that follow a name are parenthetic and should be punctuated accordingly.
Eg: Letters, packages, etc., should go here.
I understand why the other abbreviations are parenthetical, but am not convinced whether etc. should be parenthetic.