These companies that update their software when updates are available from the vendor... do none of them apply the update to a small number of machines, check for problems in their own circumstances and only when satisfied that there are no such problems, roll out the update to a larger set of machines and ultimately to all machines in the company?

For such a large number of very large companies worldwide to fall over, the only possibility is that they all have incompetent systems administrators.

I don't believe it.