Some people will know that the idea sucks, but they won't say so because if they did then nobody would like them. Why should they stick their neck out just to shoot down an idea? For the sake of the company? Pfft, no way. After all, it's not their company. They love working there, but it's not like they built the company from scratch in their garage or something. If they don't get along with people at work, what's the point?
And besides, Apple is so successful that it can absorb a sucky idea or two. Or three. Right?
Saying no is a big part of what makes Apple great and Steve was the guy who could say it. I don't know how he did it. I mean, eventually he could do it because he was Steve Jobs but I don't know how he did it in the first place. Who can do it now? Who would want to? It's irrational.