I don't see how either of those systems require explicit gears, just that machines run at different speeds with different power supplies (and the gearing is abstracted).
... and neither do I, for that matter. Explicit gear system has its merits, of course, but none of them are really that important. I'll list them at the end of my post for no apparent reason.
I understand that real life applications can require a lot of work to do these things, but is there a reason that handwaving at the 'mechanism' requirement is not sufficient to cover this?
Mechanisms are, in my opinion, an excelent but temporary solution to all mechanical problems. Just like bookkeeping without leaving the office or telepathic work orders. They work well for now, but eventually (even if it is in five years time) will need to get some attention.
And now some not-so-important reasons for implementing gears:
1. A whole new source of Fun for less careful dwarves.
2. Complex gear system below a retractable bridge can provide the fortress with a whole year supply of goblin goulash.
3. Should the game ever support multi-tile gears, they would look really cool in a fortress. Also you could stage a dramatic duel on top of one.