Apple has staked their reputation on the line and said "send us an NSL if you like, we have nothing we can give you". And the cryptographic principles, if executed properly, are sound.
Maybe they're lying. Maybe Snowden 2.0 will come out next year and tell us the truth and instantly destroy their credibility. That's a gamble I wouldn't take with my company, but it's plausible.
See I figure, if you're a threat to National Security, the NSA still has options. They just don't include monitoring over the wire or asking Apple or Google for it.
edit: The Intercept article [4] you mention above suggests to me more that they aren't yet finished implementing it properly and less that they are lying. I would take it as a work in progress.