These polls never really achieve their goal of showing who really is the best driver of all time, in my opinion. The main reason being because Drivers, cars and times change...
Think about it. Clark and Moss, and their contemporaries such as Brabham, raced in a time when gentlemanly behaviour and a good race were most important. The cars were dogs to drive by today's standards, and the possibility of dying while racing was almost a given.
Drivers like Stewart, Fittipaldi and Lauda were at the height of their powers in the age of experimentation and innovation, when slick tyres, downforce and turbocharging were just being discovered and exploited. Sponsorship was coming into the equation too.
Piquet, Senna and Prost came to the fore when F1 was becoming a commercial entity, and the cars were at their most powerful and racy. Brilliant drivers though they were (I'd still be hard pressed to drive one of those 1000hp turbo cars in reality even if you paid me millions :tongue
, part of the reason why I think they are revered so much is because they were more exposed to the public than anyone before them because of the sport's newfound commercial prowess.
Finally the drivers of today, including Hamilton, Alonso and Schumacher, are racing in a world of social media and the internet, where more people can discuss them and their inticate details than ever before. The cars are developed season in and season out, with improvements being made even during race weekends, a far cry from the early days when manufacturers would often use the same car model for years at a time.
Every driver, or group of drivers from a certain era, is different. The conditions under which they competed were very different, and so we see different sides of what it takes to truly be one of the greats. Therefore, in my eyes, there is no greatest F1 driver of all time, there never was, and there never will be.