One reason for more frequent brake fluid changes on the LEAF is regeneration only works when the battery is partially discharged. On a long downhill run, regeneration may become insufficient to help slow the car so the friction brakes must be capable of keeping speed down. If the brake fluid has moisture in it, the moisture will boil as the brakes get hot. This will cause brake fading or worse. Since oil floats on water, moisture in the brake fluid will tend to collect at the lowest points in the system (which are the calipers). This makes it more likely to boil that moisture on long downhill runs. By recommending annual (or every 2 years) brake fluid replacement, Nissan minimizes their liability for loss of braking due to moisture in the fluid.
I generally have the brake fluid replaced every two years when doing the annual battery check because my dealer offers me a discount. The price my dealer offers is low enough that I would rather let them do it than go to the trouble of doing it myself. Even in my dry climate, I notice a difference of pedal feel after brake fluid replacement (pedal is firmer with new fluid).
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015; traded 8/10/2019 at 82,436 miles
White LEAF 2019 SL Plus purchased 8/10/2019