As far as how many hours you have to put in, it really depends on a few things. Mostly how well the shop is run in general. If you have "amateur night" every night, you can probably expect to be paged more often than not.
Do you think this trend will continue as newer versions of Oracle come out that are easier to manage?
I believe so - Oracle will continue to be used on large applications - where the business needs to get every bit of performance out of the database. Also things like SOX and PCI make life difficult for businesses without a strong DBA.
I don't equate being easier to manage with not needing a DBA, but I do think DBA positions are changing - we have to know more about the business, more about other software & infrastructure. Again - just my own experience...