I've never heard of flights being changed like yours in #1 without you being notified. Only time my flights were automatically changed like that is due to a schedule change that would have resulted in a mis-connect. Do you have all your proper alerts set up on CO.Com? If so, you should have gotten an email or phone call about the change. I have those set up, but recently haven't gotten my alerts.

Regarding #2, xyzzy is right. Been a policy like that for years. If you don't begin your trip, you can't finish it. Where the real trouble comes is when you get moved to another airline and the GA doesn't properly update the system and your return is cancelled. Had this happen a couple times and ended up once getting a $500 voucher for an involuntary bump out of it