So your extra 10 kg would cost me about $20 more. At retail that would be another $100 or so. In other words, making it 10kg heavier would sharply increase the price; it would also be for things that aren't easily visible to the consumer. Your competition would destroy you.
Source: I own a factory.
Of course if that 10kg of steel was on the drum, the stationary mass would need to be increased as well. But I doubt washing machine drums are really a high failure part, so a hypothetical "10kg of steel" is a useless in the context of a washing machine.
It's hard to make a comprehensive argument about entire machines when the problem is designers having a principle agent problem for every single part.
It's been a while, but I remember when the transition from pull tabs to "pop tabs" occurred; at first (IIRC), the "pop tabs" were solid, but it wasn't long until they became hollow as well.
Of course, that led to some problems which still exist today (though not nearly as often). The biggest one being the balance between the strength of the tab, vs the opening part (whatever it is called - closure?). In the past (and occasionally today for the odd soda), you could pull up on the tab - and it would bend or break off, without opening the soda! Simple enough to fix (do not press down on the opening with your thumb!) with a butter knife or some other similar tool, but annoying at the same time.
That said, my BMW is at 147k miles without a clutch replacement, and it's lived a pretty hard life (track events, etc). In fact, in 20 years of driving, I've never replaced a clutch in a car I owned, and I've never owned a car with less than 50k miles (well, okay, I just bought a brand new car last year, so of course its clutch is still going strong).
A new, mass-market quality (e.g. Honda) car made in the last decade will easily go several 100K miles if given basic care, and will probably not have any major problems or be showing much if any rust in that time.
