Technically they haven't - the FIA technical delegate (Jo Bauer) has performed scrutineering, and decided not to refer the system to the stewards. In situations where Bauer finds something out of order (such as Sauber at Melbourne last season), it is referred to the stewards for a decision.
If someone protests with a specific question, the stewards will take advice from Bauer and Whiting and whoever else, but still the ruling on the protest will be down to them. Until then, they won't look at the car directly.
EDIT: for example:
Have to disagree.
Technically they
have passed it twice, Melbourne and Malaysia, three days before the race.
If they hadn't passed it at both those venues then there would have been no Mercs on the grid.
In addition Charlie Whiting has reportedly considered multiple complaints by other teams and knocked them back each time.
I also read somewhere else that the FIA approved this before Mercedes even built the damn thing but I haven't found a link to anything that shows that one way or the other.
The Technical Delegate's report makes interesting (!) reading. Here are some nuggets gleaned from it.
At Malaysia, car 7 had the symetric front wing deflection test
Car 7 also had tests for
1) Bodywork around the front wheels
2) Front wing height and overhang
3) Rear wing height and overhang
4) Front and rear wing width
5) Rear wing configuration
6) Rear bodywork area
7) Rear winglet height
8) Skidblock thickness
9) Stepped bottom
10) Diffuser height
11) Diffuser area
12) Overall height
13) Overall width
[5 and 6 are my italics]
Also car 7 (again had:
It was confirmed for car numbers ...,07,... that any vertical cross section of bodywork normal to the car centre line and situated in the volumes defined in Article 3.8.4 form one tangent continuous curve on its external surface with a radius no less than 75mm.
The concave radius of sections of the three rear wing elements which are in contact with the external air stream was checked on car numbers ... 07,...
The bit at the end above Jo Bauer's signature is that all cars tested in these tests and for weights were in conformity with the 2012 FIA F1 Technical Regulations.
Well done Mercedes.
Let's see you do something with it now !
One solitary point from two races is not good enough even if the car technically is !