They didn't have an established mark in the mobile phone market when they entered it either- and that venture seems to have worked out all right for them...
Cellphone manufacturers were caught off guard by the time iPhone and iPad was released. They never think to seriously market a full touch based devices without stylus, turned out they sell like crazy. Who would've known?
Admittedly, it was a great great success. It was once in a lifetime moment for Apple.
But now, I don't think competitors would put themselves caught off their pants again in the same situation with TVs.
But even then, OEMs learn from their mistakes, even the mighty iPhone and iPad starts becoming "just another" mass marketed smartphone and tablet in the technology jungle food chain nowadays. They're still great and appealing but market also starts to be flooded with great alternatives.
Now about the TV business, a slight rumor about Apple flatpanel TVs have made Samsung and friends rushly jump in to Smart TVs business and squeeze out all their possibilites. TV apps, smart gestures, wireless display and sharing, built in browser, quad core SoC .. basically giant tablet on a stick. As much as I hate "smart" TVs, half baked apps and their pricing options, I think they've saturated all the possibilities to make flatpanel TVs revolutionized.