Well, that's exactly why I mentioned not being a native speaker... I do that kind of mistake (and less subtle ones too), and I don't want you to think that I'm just ignorant or something.
Believe it or not, mistakenly substituting the word "less" when the correct word would be "fewer" is a mistake that a lot of native English speakers make.
Good to know... and now I'll try to be careful with that too.