The same can be said for any team.
And it's highly unlikely that we have 2 starters on the DL at the same time.
When two of those starters are Strasburg and Sanchez, neither of whom has managed even 30 starts in any of the last four seasons, it seems rather likely that there would be a second starter out at the same time. You're talking about dudes who each miss a month of each season on a regular basis. If you take them each missing 1 month of a 6-month season, you're expecting to have one of them on the DL literally a third of the time, assuming their annual DL stints don't overlap. Add in the fact that the two primary candidates for #5 are both also perpetually injured, and you really heighten the possibility.
Roark and Gio weren't tremendously effective all the time - or even most of it, last season at least - but one thing they both did was take the damn ball every fifth day. That's something in short supply in DC right now.