I'm not sure parents are good judges of their kids' abilities. At least in some cases parents can be way off. I was one of those parents. I really didn't think DS was anything special, I knew he was smart but didn't really think too much about it. When he entered K, when I saw what the other kids could do, in our great school in our great district with many type A parents, I was totally shocked. That was when I realized that DS was soooooooo advanced.
On the other hand there are parents who sent their kids to K with full confidence that their kids would be the best in school, only to find out that their kids are pretty average.
I think the lack of research and careful observation by parents could be the reason.
On the other hand, I also don't get it at all why people make a dichotomy of giftedness vs. hard-working. How many parents of gifted kids actually believe that effort is not necessary? I've never met one. This kind of statements only increases people's prejudice against gifted kids and their parents, and I think it's utterly unfair.
I have always communicated with DS's teachers about acceleration from the point of view of making gifted kids put in efforts: if they are not challenged, how do they learn to take challenges and how do they learn the value of hard-working? But I'm really not sure whether we can overcome the strong prejudice.
