Disclaimer: I do not speak for my employer, and their views may differ from my own.
Well, obviously no it wasn't. Pascal Klien worries about the inability to sue Microsoft over the failure of Botany Bay customs computers here in Australia. As a software engineer who works in industries where the kind of money he mentions are thrown around I can tell you that the operating system is usually not the hardest working component of the system. We still do a fair bit for our money. I can tell you that whether we were delivering on Windows, Linux, or Solaris the hardest working pieces of the operational system will be hardware and our software rather than any commodity operating system. The OS provides a few essential commodity services, but it doesn't have any great influcence over system performance in even moderately complicated systems. It doesn't greatly affect scalabilty. Most scaling and performance capability comes down to how you structure a cluster of several machines rather than how any one piece behaves.
Not knowing all the finer details of this case I find the chance that the operating system played any direct role in these problems remote. I also find the suggestion that not being able to sue Microsoft for failures is a little absurd coming from a free software advoate. Should Linus allow himself to be sued when Linux is used in mission-critical applications? Surely not. It is the responsibility of the contractor who sold Customs their new computer system to make sure there are no problems, and you can be sure they are both sueable and that they have sufficient insurance or collateral to pay out any claim. That's assuming that Customs gave them accurate and appropriate specs. If not, then Customs is to blame here and the contractor should be being loaded up with money sufficient to have come in and save the day.
If a contractor chooses to reduce their costs by using commodity software such as operating systems in mission-critical environments they must also bear responsibility for the adequacy of that software in their own operational profile. Writing their own operating system is almost certainly counter-productive for the kind of system being examined here, and as far as commodity operating systems go Windows has a long and sufficiently good track record in many industries.
Benjamin