Yep, they wanted to avoid the "super duper character" business of the last few games. So they made class changing pretty strict.
And yeah, a rogue->ninja switch would lose the backstab, and bard->gadgeteer would lose the improved camping ability.
You have to think a little more about your party this time around. And don't be surprised if you find yourself starting over with several different groups. We've all been down that road
Nightowl2