I think for the average to beginning angler the fact that Power Pro is such a popular name in the industry has a big impact on why so many people claim to fish with it. Heck, you can buy it at any sporting good store, its not like you are forced to go to a tackle shop to buy a spool. The fact that they are owned by Shimano also helps make them so prominent.
I personally see nothing special about PowerPro, I have used it, and was not impressed with its casting abilities. It's not a bad line, just nothing special.
The product that I stand behind is McCoy's braid. It cast great, cuts through kelp in the salt, and can rip a large mouth out from inside a brush pile. It is also made in the USA. I refuse to buy a foreign car... I like the same principle with fishing line.
http://www.mccoyfishingline.com/news...e_braided.html