I find it really ironic that Google, a company so used to being the new hotness upstart company, is so willfully ignoring usage patterns of a significant minority comprising "the youth" and people on the wrong side of the internet divide, and much of the third world, and anyone without a data plan outside of wifi range.
What these people have in common is they use sms or some form of text-like DM instead of email, so email notifications sit in an unread inbox and are effectively useless. Syncing calendars is fine as long as each individual maintains their own calendar, but sms is one of the nice ways to notify individual attendees without some major calendar confab.
For example, my kid's french tutor uses Google calendar for scheduling, and if you load the calendar it shows *every* person scheduled on that calendar, which is great for finding available spots, but it's not something you would leave visible. Turn it off/non-visible, and you lose web notifications. However, at present each person gets an sms notification for their appointment, even if they turn the calendar off. Sooo.... Google expects every person on a shared calendar to leave that calendar active at all times in order to receive web or email notifications, which are likely ignored if not disabled?
It's a tone-deaf move. Personally, I use sms to ensure my kids get the notification no matter what, and this downgrade will result in all sorts of ignored events and missed appointments. One workaround, at least for t-mobile, is to email the notification to 800YOURNUM@tmomail.net