This is an historical hairstyle/haircut. It's possible that it's seeing a greater (and more exaggerated) appearance in costume dramas because of its current popularity, or vice versa.

From the beginning of the 19th century, the standard for men's hair was to be fairly short - in comparison to the styles of the previous century - and brushed forward over the temples and forehead, generally parted to some extent on one side. This portrait of a Captain Graham is an excellent example. It was known as a cut à la Titus, as it was an imitation of styles seen on Roman statuary (although I've yet to see a bust of Titus himself that looks like this). Over the course of a few decades the cut became smoother, with the part more defined, as you can see in this portrait of Frederick Thesiger. This essentially defined the standard men's haircut for the rest of the century.

The version where the hair was slicked straight back instead of to one side (sometimes with a subtle center part to it) doesn't turn up until after the turn of the century, and it was rarely shaved so close at the sides. This garter advertisement represents the sort of man with whom it was strongly associated: young, collegiate, and athletic. It aged up with them, and in the 1920s and 1930s men of all ages might wear their hair combed back.

However, the hairstyle was not as prevalent as the side-parted version, and it seems to have died out during the 1930s. By WWII, a man would probably not have been wearing it anymore.