It's a bad habit to get into, but it can be broken. Try using a light radio station or a fan instead.
I need some type of circulation or light sound, so I have a fan running on low at night. But sleeping with a tv on can be difficult, some shows may be loud, others may be quiet, so after the quiet if a loud noise comes on it can wake her back up. Also, being dependent on a tv for sound can't be healthy, here's some research on the subject:
When there's light, your pituitary gland produces saratonin, when it's dark, it produces melatonin which is what makes you sleep. The light from the TV can make you produce less melatonin resulting in troubles sleeping.
The correlation between sleep and the TV on is simpler than that- too much noise to get deep REM sleep, and the eyes pick up the flickering movements of flashy lights. Turning off the TV does not save melatonin, it's just a good idea. (Although, many people swear by the "white noise" of the TV, and the comfort of background noise helps some people feel as if they are not alone in the house, and sleep better as a result... go figure!
All of that aside, we won't have tv's in our rooms either, so much research has been done that it can be distracting and confining and unhealthy but that's up to each family.
The New York Times reports on several disturbing statistics connecting televisions in the bedroom to health and developmental problems like obesity, insomnia, and more. The article focuses on the effects of the bedroom TV on kids (who see lower test scores and are at a higher risk of smoking), but we've also seen how electronic media can hinder a good night's sleep for adults, as well.