PH testing, and Alkalinity Questions

[Myka]

Ok, I've found this interesting...

Many people believe it is "general knowledge" that Salifert is 2 dKH higher than Elos. Most people believe Elos over Salifert.

In the mid 2000's in the USA it was popular to keep alkalinity at 9 dKH. The most popular alkalinity test kit? Salifert.

In the last few years it has become more and more popular to keep alkalinity 7 dKH. Interestingly enough Salifert is losing sales as Elos creeps into the market.

NSW alkalinity values are usually around 7.0 dKH (Randy Holmes-Farley).

Is this all coincidence or just works from my particular perspective? Opinions are always relative. I'm not the first to notice this interesting trend though.