They may not be extra rare, but they are rare enough to meet the technical definition of the word. This is compared to Mac Cube systems which are really common,

They may not be extra rare, but they are rare enough to meet the technical definition of the word. This is compared to Mac Cube systems which are really common, all things considered. Only around 50,000 units were ever sold. Even the Amiga, which is rare by today's standards, sold around 100x as many units. The Delorean is considered rare with only around 8,000 ever made. It's all about degrees.