Nonsense. Even business owners get to act crazy once in a while, let alone racers in their early 20's. Not to mention having a personality goes a long way in doing your PR, it is very important from a team owners point of view to have someone sociable and interesting to the media. Racing is an commercial activity, heavily marketing related, if someone is not able to do anything except racing on track than its sponsor is not getting what its worth translating track success with brand building.
The reality is, except for the 3 or 4 championship challenging teams, race result isn't the definite matter, a mid field team can survive comfortably with occasional point finishes as long as the commercial side is played right, a lot of companies want to associate with formula 1, but not everyone one of them wants the "we are the winner, we are the best" angle, not every sponsor needs a winning driver - good results are welcomed of course, but not mandatory, there are many cases where driving ability isn't the first priority in a driver making into F1.
As fans, some of us like the strong and silent type, however just reading the complaints about faceless corporate drivers in F1 racing fan mails section for so many years, I think the majority of fans like drivers with a life. if the fan wants it, than it is perfect business sense to have it.