Brake fluid flush is a recommendation. If your system stays closed and does not allow moisture to be absorbed into the fluid; it is usually a non-issue.
The two year normal driving or one year if in a severe driving climate is not unique to the LEAF. My 2002 MB SLK-320 and my 2004 VOLVO XC-70 have the same reommended service intervals.
Personally, I do my own flush with a power flushing uint and use ATE Super Blue Racing Fluid because it far exceeds the properties of the standard DOT 4 brake fluid. Oh, yes, this great fluid is not considered unacceptable in some states as is BLUE in color vice yellow.
I flush ever two years because more than going, I like stopping!