One could open and close Notepad and Calc all day long and even do some light websurfing with IE with no problem, just to find the system bogs down trying to work with a real productivity app like an IDE, a video editor, or even a spreadsheet.

I think we've all seen a slow desktop before. Windows generally has minimum requirements well below that which you would want to have for serious productivity work. An OS has to leave some RAM and storage space for the user's apps.

This is why when someone says "It runs XYZ!" I presume they mean it runs it well enough that it doesn't get in the way under general usage.

People sometimes take liberties with claims about what runs on what, but generally do follow that guideline.