Yes, there have been plenty of instances of downtime aside from the HR datastore - e.g. memcache and task queue have both gone down simultaneously and for more than an hour, which can be hugely disruptive but don't count as datastore outage.

Also, there are lots of instances of localized downtime that doesn't make it into the global system status - you only have to hang out in the IRC room to see people coming in with "is anyone else seeing really slow startup times" or "is anyone else not seeing logs updating for the last hour".