This is a good point, but the DJIA has booted out one stock and replaced it with another about 50 times during its history. It does this when an existing stock is deemed to no longer be sufficiently representative of the type of tracking the DJIA intended to maintain, and another is found that is a better representation of the DJIA's mission.

Tiobe may also update their data set from time to time, but if they do, they've somehow allowed it to lose relevancy anyway.