For those of you who have not bothered to listen to the ATC recordings, it is notable that everyone calling for start clearance was also de-icing. I don't think I heard one flight except the IB flight that didn't require de-icing and request pushback from the gate to allow it.
The clearance delivery person repeatedly asked the Iberia flight if they had "already de-iced". They also asked again, "do you need to de-ice?". Each time, the IB pilot said "negative". It seems that the controller had some concern about the lack of de-icing judging by the number of times he queried the IB flight.
The BA pilot then made a clear request to pass on the message to the IB crew that they had seen the top surface of their wing covered in snow and would ATC pass on their concerns, which they did on the ground frequency. The IB pilots had ample time and opportunity to check the condition of their wings and to de-ice. They chose not to when it was pointed out that they had "substantial" amounts of snow on their wing and it was quite obvious that everyone else was de-icing.
As has been pointed out by others, you just do not go with ANY snow on your wings because you do not know what lies underneath it. It does sound as though this IB crew were "cowboys". That does not imply that all IB pilots are, even though the original title of this thread implied so.
Hopefully, if this thread is brought to the attention of their managers, the pilots concerned will be reminded of the requirements to de-ice whenever there is any frozen deposit on the upper surfce of their wings. I'm pretty sure that the adverse publicity that this thread has caused them is in effect more expensive than the cost of the de-icing the pilot thought he was saving the company at the time.