All macs have some sort of magic incantation to reset their key variables, NVRAM, PRAM etc. The boot video resolution is one of these variables. When cleared, it defaults to something extremely common that is likely to work with any display.

The incantation is different from mac to mac. Sometimes it's reboot while holding down cmd-opt-P-R. For the last couple years, it's been power-off, remove battery if it's a laptop, then hold down the power button for 5 seconds.

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The incantation is different from mac to mac. Sometimes it's reboot while holding down cmd-opt-P-R. For the last couple years, it's been power-off, remove battery if it's a laptop, then hold down the power button for 5 seconds.

Clarification: Command, Option, P, and R for resetting PRAM and NVRAM works on all Macs: 68k, PowerPC, and Intel
http://support.apple.com/kb/HT1379

Removing the battery and holding down the power button for 5s resets the SMC but it only works on some specific machines. And it should not be done arbitrarily regardless what Mac we are talking about.
How to and when to reset the SMC/PMU on Macs of this decade is explained here:
http://support.apple.com/kb/HT1894

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