I currently have 4 Windows PCs (2 WinXP, 1 Win2k, and 1 NT4) that are at this moment over 47 days uptime. All four of those machines have mIRC installed. Additionally, I have another machine that is at 42 days right now. I also expect my newly setup Windows 2003 machine to break 47 days no problem.

So where exactly are you getting this statistic that no non-server Windows PCs have uptimes greater than 50 days?