Technically the Amiga Platform has always been rather agnostic about it's timing & video output. It spits out PAL / NTSC / RGBS in various funky resolutions, all you have to do is ask or set a jumper depending on the model. Secondly if it wasn't for this spot on NTSC carrier frequency that the Amiga could output we would never have seen products such as the Video Toaster. http://en.wikipedia.org/wiki/Video_Toaster
Vaguely related, is that I once hooked up a monochrome VGA monitor to my Amiga 1200 by soldering the monitor's cable to a suitable Amiga video connector, and setting it up to be 640x480 VGA in the OS settings.
To be fair, the A2024 had a refresh rate of 60hz, but due to the way it "multiplexed" 4 screens, it had an effective refresh rate of ~15hz (60/4). A much different, and less interesting reality.
I don't think the first generation Amigas were that agnostic. You had chip RAM that was tied to video timings and fast RAM that wasn't. That indicates the motherboard timings were very coupled to the timings of the video generation circuitry and the dedicated chips.
Or this oddity, the A2024 with a 10hz-15hz refresh rate: http://www.amiga-hardware.com/showhardware.cgi?HARDID=863