Of course you are right that no sane person would contemplate this calendar for any purpose other than user-facing display, and even then only where it is absolutely required.
But the insane WTF thing is that it does still seem to be widely required on any kind of financial document. Expense reports, salary statements, that kind of thing. All my banks use this format (and also SJIS text encoding when I download my data (T_T)...)
There are also lots of internal processes^W^W Excel spreadsheets in active use that expect these values so I've seen more than one program that converts 2013 to "H.25"... and it's literally impossible to represent a future date, since we don't know when the emperor might die, even if we have a projected abdication date.
I can't be too smug about it, since I'm American (miles and feet, anybody?) but it is... objectively non-optimal.