Why doesn't my TV realise that my VHS is playing widescreen pictures?

When I turn on my DVD player and play a DVD my TV knows that the picture is widescreen and the TV displays the Widescreen picture properly. My SKY box is also displayed properly. The TV displays both a 4:3 and 16:9 picture properly.

My VHS player is not displayed properly. If I playback a Widescreen TV programme which I have recorded I must switch my TV to Widescreen, otherwise I will see a 4:3 area with tall thin people.

Why doesn't my TV "know" that the picture is either 4:3 or 16:9?