The point? You still maintain your depth. Say you do that, you risk exposing Cecil or Rogers to the waivers who are surely to be claimed, Happ gets their spot. Josh Johnson goes down and now you need Happ to fill in that spot and all of a sudden, you are short of a bullpen arm and calling up guys like Dyson/Crawford. What happens when there are multiple injuries? This is why you need depth, its not fair sometimes but it is what it is when you have options. Look at what happened to John Lannon last year, he is a similar pitcher to Happ who started the season and spent most of his time in the minors because there was just no room for him and he was a guy that deserved to be in the majors (he was also making 5M in 2012).
Cecil isn't as bad as some make it out to be either. He sucks as a starter but I don't see any reason why he can't be a great reliever or at least a very good LOOGY. His stuff plays up and it allows him to focus on fewer pitchers... maybe he turns into the next Casey Janssen. Terrible as a starter who had huge platoon splits but is now a great reliever who doesn't have platoon splits anymore. Scott Downs was a terrible starter as well but turned into a great reliever who was elite at getting lefties out. Oliver was a poor starter as well. No sense in wasting a asset when you don't have to.
I've also said Delabar is an option to be sent down if there isn't enough room so it isn't like Happ would need to be sent down.