It depends on the industry. In the Ad Agency world, you're job is only as good as your last client, I've been on both ends of that - seen good, competent teams fired because the client's choices didn't work out, and have worked for companies that fired a team from an ad agency for screwing up, and that team were all let go. It's why I decided early on to not work in that industry anymore, it's too much of a rollercoaster. The people I know who stayed change jobs almost yearly these days, they just go from agency to agency. The good ones eventually set up their own agencies and get protected from getting fired by being the boss. The same is true in consulting, law, many industries, where your job is always on the line.
Gaming, it doesn't seem to be that way, and as it's been noted many times, Blizzard tends to hang onto people for a long time, which creates problems for advancement. Sadly, this is not standard in a lot of industries. 2 years is considered a long time in my job (art direction/senior designer).
I would bet that most firings at a company like Blizzard are from abusing perks, like giving away game codes and beta invites, blabbing their mouth over upcoming content that is secret, or inter-personal issues and personal issues.