They are on a lot of cars because they are old, reltively few people are buying them new now
Sit down and compare the features and you will find that the power FC sucks ass compared to the new haltech series, the links, the vipec, wolf and indeed adaptronic
And every tuner i have spoken to in Brisbane has tuned adaptronics and comment that its easy as piss! Kai zen garage like I said installs and tunes them for $1100 , look on the secret drift forums and see how many people are using them, they are also very popular in the US for the 'miata' crowd.
If you look objectively at the features im sure at the very least you will find Power FCs are gay, and in all likelyhood you will find that in a 4cyl application adaptronic cant be beat, especailly given the price
The datsun 180b was the highest selling car in Australia in 1973...doesnt mean its anygood now