Alright, so that's not quite true. Someone cares. Both Yasuo Ohba and Tadayoshi Funaba cared. Anyone dealing with historical dates that use the Julian Calendar probably cares.
However, the vast majority, I'd guess over 99% of rubyists, do not and should not care. And why should 99% suffer to make the job of 1% easier?
Wouldn't it be better to have separate classes that handled older calendars? It's not like handling both the Julian and Gregorian calendars handles all cases anyway.