Antoine,
Thanks for your comment and I agree with you that one have to be careful about what conclusions to make on these things.
That said, I did check the distribution of OS against other sources where you aren't asked by default to be tracked (i.e. visiting websites) and the distribution here is the same.
But I honestly do not think in this day of age Linux users are more security concerned than everyone else; of course there might be a higher concentration of them but I don't think the amount of users is different in windows and OSX users (at least not statistically significant).
1366x768 -> standard resolution on laptops and many default sold screens today.
What we do use these numbers for are 'trends', i.e. the Java 7 trend (slow in comparison to what one might think), Screen sizes (smaller than you might think), OS distribution (OS distribtuion have been rather stable for 2 years and Mac's are not *everywhere* in the industry, Windows is), etc.
Just to remind yourself that what you see day to day is not what the whole world sees ;)