I've used firefox like.... A LOT !....now the point I want to make isn't that I know a lot about it, sure I know something and it took a lot of time. The point is that I don't know Opera well enough to make a remote statement on what is the best. I would end up reviewing my lack of objective view.
I could never quickly surf as much with opera as I did with firefox for the sake of the review? That would take at least a year. I would by then have no idea what cool firefox extensions (or even versions) are available. It's pretty hard to find em today, now lets not look for a year? This would not do any good to the review. It would make a little more sense as it would now but it's still complete nonsense!
This is why I use/test web services, I could make/set up my own web service but this would mean I have to drop the clue on what is happening like the M$, yahoo and google developers. I'm not saying they are not the best developers, I'm just saying it also means they can't keep track of what others do.
The average user knows more about the product as the developers. Because developers develop and users actually use.