Not_another_pot, the post related specifically to C172 series and no other.
You're correct re. 100 series Cessnas all using hydraulic pressure for gear extension.
But since you raise the point...
Many other types don't. Think of the typical Piper single mechanism: Remove hydraulic pressure & the gear free falls. Alternatively, the Beech Bonanza (& Baron) series uses a mechanical drive. Alternate extension involves disabling the electric motor drive & substituting your own muscle.
Piper's PA23 series involves a manual hydraulic pump (which requires hydraulic fluid, same as the Cessna 100 & 200 series). The only difference is that it's a direct replacent for the electric motor, unlike Cessna's 'gear extension only' system.
NB. The PA23 series also has the option of a nitrogen 'blow down' opton as well. If that doesn't work then even a gear up landing only screws the gear doors & possibly the props. I reckon the designer must have had a few too many 'gear up' frights!