Google and Apple both have integrated calendar and email systems. They just use separate apps instead of having everything in one silo.
Ironically, one of the biggest successes I've seen with Google Apps is a site which had formed from multiple company mergers, with separate MS AD/Exchange domains, which 1) couldn't be merged and 2) couldn't exchange calendaring information.
The solution (this a few years back) was to go to Gmail and Google Calendaring. Among the most successful and enthusiastically adopted mail/PIM migrations I've seen ever.