Two goals from substitute Jimmy Keohane settled the contest but it was not until the Irishman's opener after 79 minutes that the Grecians had a shot on target against a stubborn and resilient Accrington backline.
Defeat leaves struggling Accrington in 21st place in League Two, with just one win to show from their last 16 matches.
Richardson said: "It wasn't a pleasant spectacle for the neutral. The two sides set up in identical fashion and we were comfortable.
"The two goals we conceded were very poor from our point of view and that is the message to the lads. They were certainly not good enough and we can do more as a group.
"We worked quite a lot this week on being solid. We were quite aware that Exeter struggle to break teams down at home and for the main part we held them to that and we had a couple of half-chances ourselves.
"Then we go 1-0 down with some sloppy defending, we go up the other end hit the bar and then find ourselves 2-0 down scratching our heads a little bit.
"We were reasonably happy at half-time, our keeper hasn't really had a save to make nor has theirs. If we didn't make the mistakes we get a result but we caused our own downfall. We need to win games, we need to get points on the board and we think we are good enough."