This is true.
I just bought my mother a new Samsung HDTV and it has a YouTube app that is very nice. But, and this is a big but, she still has to access it with her remote. No keyboard. No mouse.
That is the killer app reason for getting a Chromecast. You can use your iPhone or your iPad or similar device to replace your clunky HDTV remote. No more UP-UP-LEFT-LEFT-LEFT-CLICK to just get one letter. Instead you just type and go.
If the TV has USB ports then you could attach a wireless keyboard and mouse to the TV. That’s what I did, picked up a little logitech unit that’s about the size of a laptop keyboard for $30 and now most (sadly not all the apps on my TV like it) searched I can do by keyboard. Of course I hardly use it, because once you get the hang of it the remote navigating through that letter field is easy, yeah it’s not as fast but you’re never doing more than a dozen characters anyway. Surely not difficult enough to make solving it the “killer app”, especially since I already solved it for cheaper.