Just because a $1 spot rate is declined doesn't mean someone else is taking less than $1 per spot. Like you stated, someone else took a lower CPM or CPP, this doesn't mean a lower spot rate.
Example:
Station A: 500 AQH (very common small market AQH)
$1 spot = $2 CPM (takes two spots to accomplish 1,000 impressions)
Station B: 2,500 AQH
$4 spot = $1.60 CPM (for $4 they get 2,500 impressions)
So, even though Station B's spot rate is 4x higher, the CPM is lower, therefore the better deal. The advertiser is paying less per set of ears.