Hi Yiannis,
I tend to add these in as an advisory to my clients because for the most part, and unless I see something specific, the results have absolutely no effect on SEO. If they wish to act on them, it is for their developers to handle.
I don't argue my corner really - never had to. I just tell them like it is - the site is rendering fine in everything and with no issues, so fix errors if you have the time and resources.
As I said, unless I spot something that is an actual problem, then it tends to just get bypassed.
-Andy