Since I have worked in a very large Video Games Publisher I give you a quick inside in what these companies deal with.
For PC Games:
Anyways the problem is not that they don't know the glitches and bugs but the problem is that most companies are under a huge pressure to have the game released as soon as possible.
So I have seen many games that we knew had issues but they were conveniently overlooked to get the game on the marked.
The problem is of course also that you are testing the games under all kinda different computer specs and with different OS etc. but there are so many different specs and settings for the PC so
its litteraly impossible to test all these and to keep an eye on all these.
For the Console:
This is a little different - same setup with the Alpha and Beta game discs (which usualy crash anyways) but the submission process is different, the games are tested with a very specific games test
script as in (in our case a checklist) take out memory card at this stage and press the following key combo to get the follow message and check for spelling and truncations (truncations are a big problem specifically when the game is translated in German).
Now the main difference to the PC game is that any console game has to be submitted to either Microsoft Sony or Nintendo when you are done testing and its stable and bug free.
They put it through their own testing team which at the end either fail it or submit it (and let me tell you you want to pass first time since there are penalties) its very very hard to pass a game first time,
there are a lot of areas you can miss - messages bugs and glitches.
It usually comes back with the attached error list and you need to start from beginning as in fix the bugs and test all over again.
This all might sound like any gamers dream
to work as a QA tester but I have QA tested Blizzard Warcraft Frozen thrown which was by far the funnest game to QA test and I had fun till the very end, however there are games
like LArry that are a nighmare to test and you are so bored the from beginning to the end - than you have games like Riddick that are fucking awesome to test.