Though we have plethora of data, information, videos, photos, wiki's, blogs, and all sorts of streaming websites, TV and radio continue to exist and it will, why?
Agreed we have abundant search engines, to get you what you wanted. But what when you do not know what you wanted. puzzled :)
when you want to spend time on other's choices you have to turn in to TV/radio. Definitely computers are capturing the market share more and more, with enhanced software's+hardware's that can store/replay/record video and audio. All the gadgets are getting merged, with computer as a central intelligent unit every electronic gadget in existence will have them embedded. Going forward as we see the trend now there is not going to be a gadget that is could be clearly distinguished as a TV or radio or a computer, they will be all in one. May be the form factors may vary.
Internet on the other hand cannot just replace the TV broadcasting quality, the TV guys have gone far in their space up to 1080P or more. But you can connect your modem to the TV and watch streaming videos and browse the net, while you can watch your regular TV programs and another member of the home can watch the TV programs on a PC/Mac sitting on the other room, while playing their favorite video games or writing C# programs.