The sensitivity of the three cones overlap. We may accept that two colours are exactly the same when their distributions are totally different. This is when observation comes in. Paints are much richer than other systems . For example, grey and brown has no equivalence in the other systems.
Computers are simple minded.
The clever bit in this standardisation is that the three principle colours would normally require a three dimensional diagram, but by normalisation , a two dimensional diagram is produced. These three points define a triangle on the CIE chromaticity diagram.