Same here. Even the cars that have dominated in the past have had teething problems during testing. These problems get ironed out during the many testing miles. In the case of BrawnGP, the car was fast and reliable from day 1 - something I've not seen...ever.
I think your forgetting its a Mercedes engine wich is known to be very reliable, and a car that has been in development for probubly 13 or 14 months... its the best prepaired car on the grid.