Unfortunately, into every server's life a little rain shall fall. Your bias may lend you to claim that your chosen platform isn't susceptible to certain problems, and that may be so, but other problems will arise, fear not. In a large single-purpose farm, such as a Web server farm, the moving parts in the OS should be small in number. These servers should do one thing and do it well; if they fail at that task, then troubleshooting the problem is likely to be counter-productive. Re-image the server and get on with other things.
For smaller infrastructures, that's a luxury.
Consider the fate of a medium-size corporation with 500 employees. The majority of the users are not pushing Office documents around, but are working in a custom Oracle application to facilitate production, ordering, and shipping. Thus, only about 25% of these employees will actually need to store files on a fileserver. Thus, the fileserver need not be substantial. The IT department is running a 2P 3.06Ghz XEON server with, say, 600GB of local storage and 2GB of RAM running Windows Server 2003. This server is definitely up to the task of sharing files and printers, and is backed up to tape via the network.
It's not really financially appropriate for this infrastructure to implement redundant systems. Two of these servers are not needed for the load, and purchasing a redundant server and a SAN array isn't in the budget. With adequate backups, recovery from a total failure will be slow, but should result in complete data restoration.
The rain in this server's life isn't likely to come from disk failure, since there's a RAID5 array with a hot-spare, and disk is quickly replaced. It's not likely to come from the users, as they're simply sharing files and printers. The rain is likely to come from the admins, and they will probably never know why.
Specifically, an admin installs Brightstor on the server. The plan is to backup this server to a locally-attached IDE RAID array to facilitate quicker backups and restorations, and permit archiving to tape during production, since the backup window was slipping into the workday. The admin uses a similar non-production system to test the installation beforehand, and all is well. He then installs the application on the production server. Unfortunately, 75% through the installation, the installer simply stops. The window redraws, so the installer isn't completely locked up, but interaction with the installer is not possible. Windows event logs show nothing applicable to the situation, and the admin prudently decides to go to lunch.