Jon_Irenicus_PL: Unfortunately, most streaming services only offer 1080p streams for non-first party movies. I don't know why many people buy 4K TV's only to play 1080p streams. Like, why not stick with 1080p if you are not going to watch content in a better resolution than 1080p/1080i? So, the voicemail copmarison is weird, since the answering machine doesn't offer anything of an upgrade over your phone, whereas a Blu Ray absolutely thrashes a Netflix stream, even if you have a 10 gigabit Internet connection!
You buy a UHD TV for a couple of reasons. Mainly future proofing. However, the major streaming services (Amazon, Netflix and BBC) all have UHD and HDR content. The other advantage is that the higher end panels tend to have better processors inside them than the cheaper TVs - so the smart applications tend to work better.
Be careful with your terminology. Blu Ray means the original Blu Rays that play at 1080. BD UHD (or 4K) are the newer, UHD ones that are capable of supporting DolbyVision or HDR10. Typically, a normal blu ray beats an HD stream from Netflix or Amazon, but a 4K HDR stream will look slightly better than a blu ray (higher resolution and HDR offset the limited bit rates of the stream). A film natively shot in 4K would look better on the 4K player, although there are open questions over whether its worth purchasing conversions/upscales. That being said, the BD UHD players are struggling to get traction in the market as both the players and the discs are considerably more expensive than standard BluRays. Bear in mind that there's still a vibrant market in DVDs!
Jon_Irenicus_PL: That's like worrying about a GPU getting busted. Has anyone here ever had a GPU go busted?
Yes. I've had one that was DoA and one that died after four years of use.