This has always been a question of WHEN, not IF, and it doesn't really matter what the cause ultimately is. (presently looking like a second stage problem)
Space X has been running it's show as minimal/cheap as possible. This has been a tremendous advantage to them in garnering business. They can undercut just about anyone. However, it is also the reason for a lot of mistakes that have happened. One of the biggest cost savings they are running is on mission assurance.
The mission assurance section was a huge part of what that whole airforce certification was all about.
A good example:
The Dragon capsule losing little experiments and equipment on it's flights. The initial flight lost almost half it's electronics, why? Because they used off the shelf electronics, and just doubled or tripled them in redundency. Without proper shielding, they went bad, and items were lost. Lots of experiments were destroyed because one of the items lost was the fridge. This somehow escapes the general press cycle because the capsule survives, thus it must be a success. All other companies have been set up to do business for a while where hardened electronics have always been the standard. Doing that front end work costs more money, but was an industry mission assurance standard that would have prevented these things. Space X didn't do it, and NASA apparantly didn't force them to.
Since the initial flight, SpaceX has been adding hardened items slowly, in a try and see methodology. This goes bad, oh well the backup worked, let's try to move it there. Or that piece wasn't critical, so we'll just hope it stays working. NASA has seemingly determined that this is an acceptible risk of losing an experiment or two for the savings in cash, and thus PR has entirely been positive, even though signs are there that there is a lot of seat of the pants stuff going on contrary to industry standards.
This is, to my knowledge, the third time we've seen problems on ascent (though the other two were able to correct themselves with that redundency I mention, so they weren't "news"). Any other company would have been under review for the first problem. The company standard has finally bitten Space X with a major failure. We'll see how they respond and if they continue to be the media/NASA darling.
Meanwhile, neither US nor Russia can get supplies to the station now? Both primary lifters have had failures in the last month or two? (Russia will probably just gloss over and send one, Space X may as well if they don't get backlash from NASA)
