Why is a third party monitor having problems a big blow to apple?
(1) Because these displays were advertised (by Apple) as being designed by LG in close collaboration with Apple. They featured prominently in the launch of the new MacBook Pro.
(2) Apple's new policy seems to be not to produce their own displays, routers, back-up drives (they've stopped AirPort development, dropped their existing display) - this is a blow to that policy.
(3) Because Apple have staked a lot on the Thunderbolt 3/USB-C port by making it the only port on the new machines (TB3 has been around on newer PCs for a while, but always backed up by USB, HDMI/DP etc.). Having a single cable to a display that provides 5k, webcam, audio, downstream USB3 ports and can power the laptop is TB3's party trick - but the LG/Apple display is the only thing on the market that currently does that. There are a few 4k USB-C displays but they can only support USB2 downstream and don't typically supply enough power to do more than trickle-charge a MacBook Pro.
(4) Its early days for USB-C/Thunderbolt 3 and Apple has forced the pace with its new machine - we've had stories about cheap USB-C devices frying machines, incompatibility problems (didn't Dell have to drop their TB3 dock?) so, yeah, at this stage in the game I'd have a preference for buying USB-C/TB3 gear from Apple's list where feasible.
Also, its kinda likely that this was originally going to be an Apple-branded product - if you ignore the black plastic case, the restricted choice of ports and their layout is far more iMac/Apple Thunderbolt Display-like than other LG products. That would also explain the interference problem: if the electronics were supposed to go in an Apple-style solid aluminium case then who needs extra RF shielding?