Not exactly true. Mine are connected to a aux fuse block. Only hot while the key is on. Works fine that way. The intelligent feature can be turned off. It's in your user manual. The unit senses voltage and vibration. If it doesn't see high enough voltage input and engine vibration, it shuts the grips down. Kinda neat.
I learned this the hard way. My bike had an older pair when I bought it. Controller buttons stopped working shorty after. Luckily I got some spare parts from another member. Changed the controller and nothing worked. After fooling around and poking this, and changing that, I gave up. It almost drove me to drinking! After giving up I happen to try it while riding. They worked! Then back at home in the shed they wouldn't! Urgh. Emailed Oxford who sent me a link to the user manual. Then I found the intelligent "feature". Promptly turned it off!
That said, there is nothing wrong with going directly to the battery. Probably better to.