I second Regulation 6's comment.
I have nothing much to add to Connetts post except to answer his question:
May I ask: is there any SOP which requires ground personnel proactively and routinely to draw the commander's attention to safety-critical issues regardless of whether the commander is or may be aware of the matter?
In a perfect world a sound idea. In the late 90's I was departing Newcastle in a B757. My co-pilot's sector, therefore he had done the walkround. Conditions were cold with light rain/drizzle/sleet. He mentioned to me after his walkround that we might need de-icing but was unsure and had asked the ground engineer to check the wings before push-back.
The ground engineer advised that we didn't need de-icing. During taxi out my co-pilot, a relatively new hire but very experienced RAF fast jet pilot, said he wasn't happy and would I mind if he went into the cabin to look at the wings from a window. When he returned he was very angry and informed me that he could clearly see frozen deposits. We returned to stand and found significant ice on the wings.
I didn't need to say much to the ground engineer after my co-pilot had forcefully pointed out a salient fact or two!
My point being that commercial pressure, time pressure (delays can ruin a stations delay statistics) or sheer idleness and complacency would all play a part. There is but one arbiter regarding de-icing or not and that is the captain.
I have in my career several times experienced engineers (a jolly fine bunch in general) being less than frank when trying to convince me an aeroplane is fit for departure.
I am fortunate that my company (British Airways) will never discipline a captain for making an honest, safety related decision, no matter how costly. If the decision was wrong there might be an informal debrief to examine how things might have been done better but nothing more. That does remove one massive source of pressure from a captain.
Regrettably British Airways and many other reputable airlines with a sound safety culture are by no means the norm, especially when one looks at countries where there is a culture of corruption and a less than rigorous attitude to maintenance and SOPs.
There is no panacea and it scares me to read some of the comments from professional pilots justifying attempting a take-off without a clean wing.