Hi, thanks for the kind words and I'm glad you enjoyed the article!
To answer your question, the European releases from the 8/16 bits era are in "PAL" format, so all the game play at 50hz or 50 fps. While for the USA(+Canada) and Japanese releases, they are in "NTSC" format, so their game plays faster at 60hz / 60fps.
For more detail per country, here is a detailed map showing what TV format was/is used in each country:
https://en.wikipedia.org/wiki/File:PAL-NTSC-SECAM.svg
The NTSC (green) is for 60hz, while the PAL (blue) and SECAM (orange) are for 50hz.