Maybe the problem is that culturally, email is treated like face-to-face talking. We often talk to each other just to be pleasant. It wouldn't be weird for someone to remind you about a meeting if they saw you, or to ask if you're going to the company picnic. Actually, it would be weirder if they just posted it on the calendar and said nothing else.

So, maybe email clients aren't the issue, people are the issue (like most problems).