Taking Skip-gram for example, empirically, input vectors of words with the same POS, occurring within the same contexts tend to be close in the vector space (Mikolov et al., 2013), as they are frequently updated by back propagating the errors from the same context words.
input vectors of words with different POS, playing different semantic and syntactic roles tend to be distant from each other, as they seldom occur within the same contexts, resulting in their input vectors rarely being updated equally.