While I do believe manufacturers should make durable and reliable long lived products I don't think the warranty needs to longer than the 2 years by law (here in EU), or 3 years offered by some retailers.
If the warranty lasts a long time some people start to treat their gear poorly and abuse it "oh I can get a fix or new one for free"
I don't think there's any evidence to support that thought: Bryston has been providing a 20 year transferable warranty for decades and I never got the idea that Bryston owners are less carefull with their stuff.
By providing a long warranty period you provide security for your customers, and as a manufacturer set a bar for yourself to make your equipment as durable as possible.
Whereas sticking to the legal standard 1-2 year warranty (depending on where you live) basically gives no incentive to make a product that will remain reliable throughout the years: To the contrary, it is actually profitable when your product fails outside the warranty period, as it provides a second chance to overcharge people for parts/labour.
I've seen it countless times: A 4000€ CD player stops reading discs after 2 years, the manufacturer charges 500€ for repairs, but when you check the service manual against the repair bill it turns out that all they did was replace a 30€ standard Pioneer/Sony laser which probably takes about 45 minutes for a trained professional.
Limited warranty is to high end audio what payed DLC is to modern videogames: charging your customers for what should have been provided all along.
And it's not like it's extremely complicated or expensive to ensure (most) of your products last for years and years: Just spend a little more on a better optical transport (Instead of the standard ubiqutous low budget Teac drive), use high quality Panasonic or Nichicon/Rubycon etc. capacitors instead of "Audio Grade" Elna Silmic , or worse, made in Taiwan junk capacitors, use quality PCB's, suffcient thermal control (heatsinks),do a little more testing, use overspecced/oversized components, invest the the highest quality foam/pleather/leather etc etc. We are talking about what amounts to petty change on a multi 1000$ component.
Even if you disagree with the above, the aforementioned problems with multiple expensive headphones are of a whole new order: Both the customer and the manufacturer KNOW their 2 year old 5000€ Stax' channel imbalance , or 2000€ Audeze's driver failure is NOT caused by abuse or carelessness. It is a design/manufacturing flaw, which should be recognised as such and remedied ASAP, including a heartfelt apology and assurance that should said problem ever rear its ugly head again.... EVER (!!!)....., it will be fixed no questions asked.
I am not a manufacturer of high end audio, and I probably wouldn't be cut out for it: I can't even imagine the shame of charging someone that just bought a 1000-5000€ pair of headphones a single dime for fixing a known issue.