it may not be your job to remind me to dose up, but I like to understand easily when my medication is out of date. Now, if you'll let me return to my gut-spasms...
On a side note to your comment about "some people don't have devices", the date is stored in a much more abstract format, this is mostly about display. And poor people with no computers still need an easy way to understand the date when it is written down, if they ever want to arrange anything together. All civilizations have calendars, we just hope for some interoperability.
Mostly because I want to get my birthday presents in the right month :-p