I'd be ok with 20% variation too.

It's going to be much cheaper to administer the sale of a single vehicle over the individual sale of each part. I'd expect it to cost maybe twice as much?

Currently I'm looking for a toothed belt for a bread-maker - best price I can find is a quarter of the cost of a new bread-maker (15€ delivered), that seems a bit ridiculous to me.

The belt was in crumbs, locked behind security screws. How many functional devices have been dumped for want of a simple belt replacement I wonder.

That's never been remotely true even with third-party aftermarket parts. I imagine if that were the law, granular parts simply wouldn't be sold by anyone.