for a reason. apple's oled is technically superior to other oled displays. that's the way with many things apple does after others did them. they let others rush their crap to you first.
This is a common misperception. Apple has frequently looked to Samsung for parts that are unavailable to Samsung uses for their own devices.
The screens have completely different resolutions and pixel densities. (The S8 has a higher density, but in a diamond pentile arrangement.)
Both screens support the DCI-P3 color gamut.
The S8 has a max brightness of 440 (manual) or 620 (auto).[0]
The X appears to have a peak brightness of 625 nits[1], although that's labeled as "typical," so hands-on testing should reveal more details.
For contrast ratio, Apple described the X as "1,000,000:1" while Samsung's is described as "infinite." Marketing aside, presumably hands-on testing will reveal true numbers in a head to head.
The original point remains: The S8 screen is lovely. The other original point seems accurate as well: The iPhone X screen appears to be something new, unique to Apple.
apple doesn't just buy panels off samsung's shelves. they have samsung produce according to apple's specs and samsung is, by contract, prevented from using apple's tech.
thinking they just put galaxy displays into iphones is just bonkers.