I'm sorry but by the time they're teenagers you should have had enough 'years' as their parents to instill in them not to sit in front of it all day.
We (finally) got a TV when I was 16yrs old - and despite the fact that I'd always "wanted" one - didn't sit and watch it all day everyday, - as I'd been taught from a very young age that there were other things to do.
It's all about 'parenting' - there are SO many different factors that affect how children and teenagers perform that to say getting rid of the TV is the only solution seems mad to me!
What about those parents who never read with their kids (or perhaps don't even own any books!), those that take no interest in their childn's developnent - I'd be VERY suprised if those who were 'researched' in the original article didn't have other 'factors' affecting their performance at school!
Our TV is on ALL day but it's only really in the evening that DH or I actually "sit down" to watch anything - generally it's just there as 'background' - (apart from Wimbledon last week but that doesn't count ). Our children don't sit down and stare at it all day (and they easily could as the 'toy box' sits RIGHT in front of the TV/DVD player to stop DS2 trashing it all).
I do know of a few children in RL who DO sit and stare at the TV all day, they're also the ones who's parents would rather stick a video on for them than let them play in the garden!
And besides - how many of us are not passively using the computer now??? And how many of you run around watching Eastenders or Big Brother?