You'd think there would be far more sighted people who missed seeing the lights in the sky/meteor shower. For example: people sleeping from night shifts, or using the metros, or even visiting casinos or nightclubs.
Aside from the people sleeping off night shifts, all those people would have had to exit out into the night at some point or another. Certainly, places like Brisbane (which doesn't have a subway system) would have copped it badly, and it goes on for an insanely long time (and appears to be unhindered by cloudy skies).
The original book mentions in passing that one area is now being run by coal miners who were, in fact, down working when the shower hit, while the first movie version has a gang of former prisoners menace the heroes. Coker (who is an early antagonist that is just trying to help the blind people, but soon realizes it is not going to work) missed it because he stayed in a coal storage room for the entire day after nearly getting caught by the police during a political meeting. And, in the sequel, there are many people in New York that managed to miss the lights, such as the Native American tribe that helps the main characters, who did it because their shaman convinced them to go down into an abandoned mine.
In the original book, it is mentioned that the lights are seen even in broad daylight (they last pretty much an entire day), and all the radios are constantly talking about the event, so it would have been weird for someone to actually miss it.
There was also bound to be entire regions of the world that were heavily overcast during the effect, possibly creating large population centers that aren't suffering from any blindness. On the other hand, the exact mechanism of the blinding is only ever guessed at. The light itself may be a red herring, with the actual damage being caused by some type of fast-decaying matter falling to earth.