Also, I think there may be some cases where a keypool address would be thrown away without a generation (like if Bitcoin crashes, or maybe even when it shuts down).
The keypool IS used for coin-generation transactions.And the way it is implemented, it should never throw away keys. If I recall correctly, there is a very small chance if you lose power or bitcoin crashes a key from the keypool could be used twice. But that has no bad effects, it is just very unusual.