Are random encounters deadlier in APs?

Is it just me or are the random encounters in APs more deadly than the boss encounters?

From the APs I've run/played or watched, random encounters tend to be deadly while the BBEGs encounters, the PCs barely break a sweat.

NOTE: "random encounters" are those encounters that don't have anything to do with the plot or move the story along e.g. theSnail on Castrovelin Gatewalkers.