All engines require no oil changes for the life of the engine provided you're willing to accept the notion that the life of the engine will be overly short...
On the plastic parts thing... I'm often hesitant to condemn a company for making a part out of plastic without researching what's actually going on because of the KitchenAid lesson:
KitchenAid as some of you will know makes stand mixers. If someone is serious about cooking, they've probably got one prominently displayed in their kitchen.
The old mixers were made with one plastic gear in the transmission. People found out about it and got very angry, because they didn't want to be paying $300 for a mixer with a plastic gear in it!
So bowing to pressure, KitchenAid started making their new mixers with an all metal transmission, and people were happy.
Well, here's the problem: That plastic gear was a sacrificial part. If someone tried to mix something that was too viscous (think large quantities of heavy bread dough), that gear would break, which would prevent the entire transmission from binding. You'd replace the gear and get on with your life.
Removing that gear meant that suddenly entire transmissions in these things were being wrecked, which means you're buying a brand new mixer instead of a cheap plastic gear.
Sometimes plastic is not a bad thing, even in places where you might not automatically think plastic should be.