To second that: perhaps somewhat ironically older LCD monitors seem to be nicer about oddball video modes than current ones, undoubtedly because when they started appearing in droves back in the early 'aughts there was still a "considerably greater than non-zero" chance that someone might want to hook one up to a computer that didn't necessarily base its decisions about what video mode it output on the list of supported resolutions announced over the VESA DDC channel. These days the manufacturers seem to make the assumption that your client is going to be polite and not try colouring outside the lines.
A specific use case I'll mention that actually doesn't even involve VGA: Apple's DVI Cinema Displays are pretty much the worst case when it comes to backwards compatibility. If you hook one up to a PC video card made before around late 2005-ish there's a good chance you won't see anything until your Windowing system loads because cards prior to that weren't smart enough to use the DDC information to pick a "supported by the monitor" video mode for DOS/BIOS messages. (They made the assumption that any connected monitor should be able to support legacy VGA text/graphics modes, which wasn't a bad assumption at the time.) I know this because when I originally received a 2006 Mac Pro with a pair of 23" Cinema displays as a company workstation I was initially annoyed enough with trying to move my workflow over to OS X and the difficulty of getting Linux on it that I considered swapping the machine for a big Dell workstation, but the nVidia cards in said workstation were useless with the Cinema monitors (which I wanted to keep)... or at least would leave you blind until X11 loaded. It did turn out that the ATI card in my little OptiPlex 280 SFF *was* smart enough to display its BIOS messages on said monitors so I actually used it for another month or so until Apple released a firmware update for the Mac Pro that had actually *working* legacy BIOS emulation allowing me to boot Linux without the gotchyas that came with using the EFI loader.
Granted I don't really blame Apple for not caring about whether their monitors worked on a PC. That's not how they roll.
A specific use case I'll mention that actually doesn't even involve VGA: Apple's DVI Cinema Displays are pretty much the worst case when it comes to backwards compatibility. If you hook one up to a PC video card made before around late 2005-ish there's a good chance you won't see anything until your Windowing system loads because cards prior to that weren't smart enough to use the DDC information to pick a "supported by the monitor" video mode for DOS/BIOS messages. (They made the assumption that any connected monitor should be able to support legacy VGA text/graphics modes, which wasn't a bad assumption at the time.) I know this because when I originally received a 2006 Mac Pro with a pair of 23" Cinema displays as a company workstation I was initially annoyed enough with trying to move my workflow over to OS X and the difficulty of getting Linux on it that I considered swapping the machine for a big Dell workstation, but the nVidia cards in said workstation were useless with the Cinema monitors (which I wanted to keep)... or at least would leave you blind until X11 loaded. It did turn out that the ATI card in my little OptiPlex 280 SFF *was* smart enough to display its BIOS messages on said monitors so I actually used it for another month or so until Apple released a firmware update for the Mac Pro that had actually *working* legacy BIOS emulation allowing me to boot Linux without the gotchyas that came with using the EFI loader.
Granted I don't really blame Apple for not caring about whether their monitors worked on a PC. That's not how they roll.