I would guess that that's all a significant number of unix-like OS users do with sed, and in those circumstances, it does make more sense to use sed than a more extensive language. For simple substitutions like that, I'd just use an alias:
alias ped='perl -lpe'
to save the extra keystrokes.
If sed has capabilities other than that, I don't particularly care... but that's one thing that I need to do frequently which is more painful in awk or python.