There is 3 types of beasts in F1.......Ferocious Ones.....Schumi,Alonso,Hamilton......Tamed Ones......Kubica,Massa,Barichello,Trulli........and the ones you keep on a leash(too nice of guys for their own good) Kova,Button,Heidfeld,Rosberg!!
The above, is no assessment of their driving skills at all,just an observation on their personalities!!! What seperates the Great from the Good is their Killer Instinct......some have it,and some dont!
I could be all wrong 
Complete nonsense. This is a really superficial way of looking at it. This isn't an observation on their personalities, this is an observation on the media representation of their personalities, or the personality those you're talking about portray themselves as having to the public. I'm a lecturer, I portray a completely different personality in front of my students than I do in front of my colleagues, and different again to how I act when with my friends. These guys will be no different. Nobody should be so arrogant as to decide that they can work out somebody's entire personality from the tiny snippets we see of them every fortnight for minutes at a time in an interview.
Button is not somebody that's kept on a leash - just look at his various early career moves when he made the decisions (for better or worse) as he thought he could further his own career. Absolute nonsense to say he's a driver kept on a leash. Likewise with Rosberg. A year before he left Williams he basically said that if Williams didn't improve to give him a potentially race winning car in the near future he would be leaving - and look what happened...
You simply can't have been following F1 log enough if you think that Heidfeld is a driver to be kept on a leash, or indeed people saying that 'he had his chance and look where he is now - without a seat'. It is correct to say that Heidfeld has had chances to prove himself (albeit in an upper mid-grid team), and prove himself he did! He outpointed Kubica over 3 1/2 seasons together in spite of consistently qualifying lower on the grid. So the question has to be asked - why is Kubica in the position he is compared to the position Heidfeld is in? The simple answer is that Heidfeld has had an unusually raw deal at a time that all of the top seats in F1 are filled, it's nothing whatsoever to do with his 'lack of ability'.
As a further note - F1's addiction to youth is driving me potty. Why is it that nowadays once a driver hits 30 they're automatically 'past it'. What a load of bull. Until about a decade ago it was common place through the history of all motorsport - F1 included for drivers to still be competitive well into their late 30's and in some cases into their mid-40's. It's not healthy this idea we have in recent years that all drivers must be 19-29 to be at the top. Complete claptrap.
Favourite racing series: F1, Indycar, NASCAR, GP2, F3, Formula E, Trophee Andros, DTM, WTCC, BTCC, World Endurance... etc. etc.