HDTV RF Modulator

Does anyone know why we haven't seen the creation of a RF Modulator similar

to the ones we've been using with our video games, cameras, etc.?  You
know 
the type I'm talking about?  Inside one end you present a baseband video 
signal, and then, out the other, comes either Channel 3 or Channel 4 which

you can connect to the set with twin lead or coax with an F connector.

It seems to me that it would be really great to have a product like this 
where one could introduce a component signal (RGB or YpRpB) or an DVI/HDMI

signal and have a 1080i/720p signal coming out on 1 or 2 HDTV digital 
channels.  Is this product not being developed because of DRM concerns?

Just curious.

TIA