The article was talking about adobe image metadata embedded in the explorer.exe executable itself, as metadata inside some png images that explorer uses in its interface.
It isn't talking about the metadata columns for files.
Read the Wikipedia article about XMP. It's a newer metadata format to Exif and IPTC. XMP comes from Adobe, it contains a lot of Adobe strings in the XML schema.
I wrote about the metadata handling in Explorer/shell32. It's a light version of what was tried out with WinFS.
Read the article again, take a look at the code. The author is not complaining about Windows Explorer being able to parse and display metadata from PNG files. The author is complaining about how much embedded metadata there is inside PNG files inside the explorer executable file itself, as well as other DLL and EXE files in Windows.
The metadata that the author finds is actually inside resources inside the executable itself. It does not include any strings found in the executable which are used to parse the metadata from other files that you have on disk.
I'm not saying metadata is cruft. Metadata is very useful during production or for managing art assets. It is however superfluous once it is embedded in an executable or other code library or packed archive. This is simply because its purpose has already been served and it is no longer needed at that point, thus wasting space.
I wrote about the metadata handling in Explorer/shell32. It's a light version of what was tried out with WinFS.