Lots of sellers separate them from the kits, thats why they are cheap. However, the kits have two warranty cards, one for the lens and one for the camera. They just did not bother to put the card with the lens.
If you need warranty service, the card is worthless. Canon wants to see the sales receipt from a authorized reseller. In the US, they have not been hard nosed about this, but with profits in free fall, they just might refuse warranty repairs.