nesdev.org

I recall there being a discussion that games that always leave all three bits turned on was because developers thought they had to do it. No idea what's the source from that, but it'd make sense at least.

And yeah, tint bits are specially nasty on the RGB PPU, since they work in a completely different way there (instead of dimming the other components, they saturate the ones set, and setting all three will effectively turn the screen white). Now, the RGB PPU gets the palette horribly wrong for starters anyway, so maybe it's not worth the effort considering support for it...

Famicom Titler and Famicom TV use the RGB PPU. A couple Famicom games, such as Just Breed, come with a warning on a package that they're not compatible with Famicom Titler or Famicom TV.