once the system is bled and topped off there is no need for additional reservoir capacity, until the pads wear. I doubt the drums were self adjusting, which would not require added capacity as it mechanically compensates for wear. But with non-self adjusting drums the brakes get worse at stopping and if you pay attention you know to adjust them.

Lucky? Nope, they either haven't run the pads down enough to run out of capacity or they are staying on top of the brake fluid level. Is it smart? Nope, lazy/cheap/ignorant take your pick.