How is DCI 2K/4K converted to HD/UHD 16:9?

[hajiketobu]

I'm very curious about how this is achieved.
I always thought 2048px are cropped to 1920px for a pixel perfect representation or simply scaled down to fit 1920px. But there seems to be more behind it. Does someone have more insight?

When you compare this 2K screenshot from Titanic published by Digital Domain with the screenshot from the Blu-Ray you notice that the 2048 x 854px (2.39:1) are cropped to about 2004 x 854px (almost 2.35:1) and then downscaled to 1920 x 818px.

2K screenshot:

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1080p Blu-Ray screenshot:

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(Notice how blurry and colour graded the Blu-Ray is? Looking at this, I think 2K movies with definitely benefit from UHD-BD.)

Also what is the reason of doing all that? Isn't integer scaling the only way to scale if you have to scale?
And btw why wasn't the UHD-BD standard comformed to DCI 4K? I see no reason of keeping 16:9 when it comes to movies. Why is television favoured over cinema? If UHD-BD is for cineasts why does it conform to television? I would surely buy a DCI 4K TV if there was content for it.