I did and all these posts I'm getting on these forums are near the level of conspiracy theories ... 

Apparently having volumetric mist at different locations and having more reflections occluded by snow constitutes as a downgrade ... 

Yeap, shading the snow is worth nothing compared to having reflections when you've gotta account for sub-surface scattering in the former ...

Yeah, that was what I meant xP

Anyway, it is advertisement, it's advertising a product to come, even as it is no claim the final build will be exactly that way, it's still a choice to falsely depict something, usually with something of a better quality than what will be achieved.

People pre-orders games, it's a business practice, there are lots of people buying that game that is being showcased, not the one delivered on its release date, several people make their choice and pay for something that'll come on a lowered quality later.

That's not right, I don't support that kind of practice and I'm all for people calling them out on those kinds of situations.
People do have a reason to do that, no need to mock them, they are not making it out of thin air.

Just to explain it to you...

The kind of effects shown in the original trailer are very hardware demanding. The low-level lighting with the contrasting bright light sources, and reflections, and glows are very nice but very demanding effects. The first trailer is clearly showing multiple "global" light sources ie; radiating light. There's two ways to display light in a game. 

a) actually have the light interacting with in game objects using a light engine.
b) hand program the shadows for specific objects that you want to be highlighted.

The previous requires a lot of work, so that light sources know how to interact with the 3d modeling. The latter requires effort for a smaller portion.

This goes hand in hand with reflections in the water on the ground. In order for the reflections to perform properly, the 3d area has to be programmed for it, and the effects have to be implemented. Sometimes, this can really bog a game down because it then has to display twice what it would show without a reflection. 

When you "change" from something that is seen as a very nice, but very code-heavy painstaking display, and replace it with a simpler, less demanding artistic choice, it is seen as a downgrade. It is seen that way because despite what your personal tastes are, the previous trailer can objectively be called a more realistic version. While the actual gameplay is still very realistic, people notice things that aren't in real life like shadows, global lighting, reflections, glow, etc. 

TL:DR 
It takes a lot of work to make a game "more realistic". So when a trailer that's seen as VERY realistic is then released looking LESS realistic, we assume they cut out features, which makes us think downgrade.

That "may" definitely means does not, don't pick a word out of a phrase to make it sound what it isn't.
The MAY makes connection to something not happening and being a weak point BUT other things are pointed as strong points.

That phrase is a confirmation of at least the Beta is not in the same level of the E3 2013 presentation, to Digital Foundry.

I just put it into italic and underlined so you can find easily where the BUT picks up the contrast of the MAY idea.

I really hope you won't go for that route of trying to using a ridiculous excuse to not to admit being wrong about something when you put me as a conspiracy theorist while trying to make a flawed point.

Yeah, I'm done here, this became nonsense, you want to discuss a word literal meaning by itself and not the actual phrase it's put into, from now on it's not worth anymore, I'm sorry, I'm also pretty sure you know very well what you are doing here.

But to answer your question , yes, if Digital Foundry mentions all effects technical quality are kept just like they were in the E3 2013 presentation and there was no downgrade whatsoever, which they already confirmed to not to be the case on the Beta as it's not matching it, I'll concede, you are right that I'm no expert in the matter, but it's even clearer that way that you don't even need one to point the kind of difference of those two.

Feel free to deliver me DF full tech review link in anyway (quote, wall, private) if you find the need to do it.

The final product is different than a mockup from three years ago? Goodness.

This is one area where developers have to be very frustrated with the entitlement of some gamers.

(Developer show cinematic teaser video)
"NO! We want gameplay video! Show us gameplay!"
"But ... but this is still early development, so many things will change ..."
"GAMEPLAY!@! STOP LYING TO US WITH CINEMATIC TEASERS!!"
"Okay, then, if this is what you want ... here is some mockup gameplay we put together using projected settings. The finished project is still years away, though, and any number of things--."
"WOW, THANK YOU!"

(Game launches)
"What the hell! This is a downgrade! THE SHADOWS ARE DIFFERENT!!"

Well then I guess we better doom every game that's going to release as "downgraded" ... 

Uncharted 4, Quantum Break, Horizon Zero Dawn, Gears of War 4, etc ...