I find it interesting that the author completely looks over Cortana when listing the various voice assistants. Cortana is perhaps the most widespread voice assistant, it being on almost every windows pc.
Windows 10 is probably on roughly 14%-15% of Windows PCs, which is some way short of "every".
According to Microsoft, more than 270 million devices run Windows 10. However, Cortana voice isn't supported in all countries, and many people have turned "her" off.
Every PC with Windows 10. I'm not sure how many there are, but it may not be most widespread or most used.