This shouldn't surprise me -- I should have thought to check this sooner. My previous (Dell) laptop had a similar (but worse) problem. The internet is filled with posts from Dell laptop owners running Linux complaining about this very thing.
But I had it in my head, for some reason, that if it were an EDID problem it would refuse to work at the higher resolutions, not the lower ones. I also put too much faith in the intelligence of monitor manufacturers. I assumed--wrongly--that since they know best what their monitors' capabilities are, they should also be smart enough to make their monitors report that information correctly.
Sadly, monitor manufacturers (or at least, the laptop ones) seem to be dumb. My old laptop's monitor, for instance, thinks it's a 1400x1050 display, when it is in fact a 1600x1200 display. And now my new laptop's monitor thinks it can run with one (and only one) video mode.
::sigh:: Go figure. I keep expecting hardware manufacturers to be sane, and I keep getting disappointed. Oh well.
Next up: Getting this laptop to suspend, and convincing the Intel video driver it wants to talk to an external monitor. Stay tuned. :p