No, MessiahWWKD, I'm definitely NOT saying that.
The specific difference is...if you have an OS...eg, XP, and you kake a skin from it, or bits of it, it remains obvious where its origins were....but that is NOT the case with a third-party skin being used in the same way.
IF the third-party skin were taken from an OS itself then things can get 'cloudy' because no-one can determine who has imitated who, both having 'copied' the OS.
WHEN and IF you wish to make use of another individual's [skinner's] graphics or work, you MUST seek and obtain their permission BEFORE you ever upload any 'derived' works to the net.....You're free to do what you like on your own computer, just not to publish without approval...