With digital its possible to transmit full height anamorphic and have the STB manipulate the image for 4:3 TVs to either LetterBox so you see the full and correct 16:9 image within a 4:3 frame, or centre cut (yuk) when a 4:3 centre image out of the transmitted 16:9 image. Naturally if you have select 16:9 on the STB the image is sent untouched to the display for correct portrial.
Note SD TV has no 16:9 frames in its standard, it only knows of 4:3 frames, therefore 16:9 full height anamorphic is the only way to transmit 16:9 images within a 4:3 system (analog or digital) for correct display on 16:9 displays.
So the end result is yes you can transmit true full height anamorphic 16:9 images on analog, however there is a functional aspect that is lacking that would p1ss 99% of analog views off, so they dont do it.
Only HD TV specifies 16:9 frames, which means they have true square pixels, SD full height anamorphic whilst gives correct 16:9 aspect ratio within a 4:3 frame the pixels at some point are rectangular.