There are a lot of question marks regarding the type of performance our offensive line will put up this year. As a particularly young unit with a lot of potential, they have failed to relieve a lot of the concerns that have been raised about them. Questions such as "Will they be able to gain experience and mesh quick enough?" or "Can they avoid the injury bug?" were not realistically going to be answered throught this preseason. Even so, the front office could have alleviated the "Is the OL deep enough?" concern with some simple pickups on the waiver wire and free agency. The fact that they didn't address this has left some people feeling perturbed, but there is a good reason to have avoided making too many waves with OL pickups.
A deep O-Line would go a long way towards easing the fears of fans, but would also hamstring the rest of the team, particularly the special teams unit. The need to address special teams failures from last year as well as throughout this preseason causes the lack of Offensive Line depth to make more sense. As most offensive lineman the Steelers would have acquired would likely not be so useful on special teams. Adding players that by all rights shouldn't see the field, even knowing that they have been seeing the field in recent years, over players that will see the field every game on special teams could be seen as irresponsible.
Most of all, the Steelers should not treat the symptoms of a problem (Injuries on the O-line) instead of treating the cause of the problem (Either injury prone lineman starting, schematic issues, or even some sort of issue with training staff have all been blamed by various people). The good news is that it seems the coaching staff has taken a shot across the bow at fixing the issues with a new OL coach, emphasis on conditioning, and a release of Willie Colon (Being a prime example of a player who clearly has been injury prone).
Most fans would agree that the Steelers will live and die by the Offensive Line this year and that does lend itself to argument that we should have more Offensive Lineman on the roster. Unfortunately, if we are being realistic, if the Steelers end up relying on a 7th, 8th, 9th, or even 10th lineman this year the odds of this team being competitive are not high, even if the front office had planned for that eventuality. This makes the gamble of relatively weak depth on the offensive line depth (Having 6 decently capable OL) a completley necessary one. One that I, personally, feel comfortable with going into the season.