I completely agree, i don't think it is appropriate for any user to declare that another user's requests are less important.
Although, what the dev prioritizes is understandably their prerogative.
Personally for me too, calendar sync is a make or break deal for an office email app. Having my phone taking care of reminding me for the tons of meetings each day takes a huge burden off for me.
As for other apps that do it, there is Touchdown, Maildroid, Emoze, Cloudmagic etc.
But Aquamail seems to do best in all respects and it would be fantastic to have this one feature added too.