I have tried my best to find something relevant, but failed. I quit Windows development almost 8 years ago, so my knowledge is pretty outdated. Back then there were still huge amounts of Windows machines without .NET framework installed. Have something changed since then? Did MSFT begin to preinstall it? Maybe there is a way to view installation statistics?
See list below
"When the .NET Framework is installed as a part of the OS, it does not appear in the Programs and Features (or Add/Remove Programs) control panel. The following is a complete list of which version of the .NET Framework is included in which version of the OS:" That being said it can be turned on or off in the "Turn Windows features on or off" section of Programs and Features.
"In addition, the .NET Framework shipped with the following versions of Windows but not as truly integrated OS components"
Back then there were still huge amounts of windows machines without .net framework installed.
Windows XP Windows Vista does not come with .NET Framework preinstalled. Windows 8+ does come with a version preinstalled.
Maybe there is a way to view installation statistics?
You will have to collect this information yourself, or base your estimations, on the usage of each edition of Windows.
Did Microsoft begin to pre-install it?