I agree. I've worked as a software developer for 15+ years and this really is not that bad compared to some of the code out there. I was honestly expecting worse..
It's all those "rockstar programmers" who spend more time reading blogs than working. Only the object oriented design pattern de jour is the way to go, everything else sucks beyond belief, apparently.
Meanwhile, COBOL code sprinkled with GO TOs run their banks and steer their satellites. The only thing that matters is if the code 1) works and 2) is readable (and most hipster frameworks fail on both accounts).
The difference between serious and amateurish outfits like MtGox is testing, testing, testing and testing. Did I mention testing? And a bunch of people who do not consider themselves rockstars or other silly things who work these systems daily.
The code isnt't testable in its current state which is exactly for the reasons already mentioned. It is not separated into components. That would have a lot of advantages, one og them being testability. The reason that COBOL works in banks is because the code has been running for decades, not because better tools don't exist now.
And OO has been questioned for a long time now with new programming languages even boosting about being non-OO.
You seem to be arguing against your own misconceptions.
I have a hard time believing that someone who's proficient in multiple programming languages would choose PHP for THIS particular job, but it would easily be the right choice if that's the only language he was fluent in.