Your laptop will never replace your TV.
That's a likely model for the big-screen TV system, too. Set-top boxes like TiVo already supplement traditional television with download capabilities, and such options will undoubtedly grow. In most cases, the quality will be lower than what comes in over broadcast. But as the popularity of today's low-fi Web video already shows, people will trade quality for convenience in some cases—to catch a missed TV episode that won't hit DVD for a year, or to watch Internet-only gems like the hilarious news blog Rocketboom.
But given the choice between the Web and traditional broadcasts, most people will pick the higher performance (and instant gratification) of traditional TV. And don't just assume that the Web will catch up in a year or two. While Internet bandwidth and video quality will improve, so will our standards. There's already talk of increasing the color gamut and resolution of HDTV. Television quality is a moving target that the Internet already fails to hit.
Séan Captain writes about technology for publications including the New York Times and Wired, and on his blog at seancaptain.typepad.com.