It all depends on the duration (i.e., value) of the note that's being counted, and your question illustrates why the numerical scale on the older-style metronomes is deceiving: beats per minute is only useful if you know what note value is receiving a nominal beat.
Consider any familiar piece of music—let's say Chopin's Funeral March, for example. It's marked Lento, and most anybody would agree that it's a slow dirge. The time signature is four quarter notes to the bar, and that might mean a speed of 40 if you're counting by quarter notes. You could, however, decide to count by eighth notes, in which case the speed would be 80 bpm. And if you were going to count by sixteenth notes, it would be 160 bpm. Yet in all cases the actual tempo remains the same; you're just counting by a different unit of duration.
Anyway, check out what note value is being counted in the metronome markings for the examples you mention. In a slow song at 160 bpm, that increment is almost certainly smaller than in a fast song at 120. It's conceivable, too, for one counted beat (i.e., one click of the metronome) to be assigned to an entire measure of music, which could mean a relatively low number for a song or piece whose tempo is considered very fast.
If this still doesn't make sense, think of how we divide a minute into 60 seconds. But a clock also has markings every five seconds, and there are 12 of those increments in the same exact span of time. If you count a minute by seconds, you are rapidly counting a large number of small increments; if you count by five-minute increments, you are slowly counting smaller number of bigger increments. So even though the speed of the counting changes (based on the value of the increment being counted), the duration of a minute doesn't.
Topic: ? about speed of songs