It's not that you're not observant. It's just the folks at GameXplain are hyper-observant, which is why they notice things like trash strewn in the streets and Midgar's window-to-AC unit ratio.
While I agree that it's best we think of the upcoming Final Fantasy VII reboot as a separate game from the original, it's nice to see the close attention paid to the original game in creating this new thing and to imagine filling in the details we never got/couldn't get back on the original PlayStation.
Things like the extra ammo clips Biggs is packing, further defining his role in the revolutionary group Avalanche. Or the Shinra troops checking out the train before the group arrives, suggesting they're expecting an attack of some sort.
For me the biggest thrill is that damn Guard Scorpion cutscene. It always bothered me that such a big enemy just appeared out of nowhere. Now it gets the intro it deserves. Makes me want to lightning the hell out of it.
What else does GameXplain see that you missed? Did you catch Cloud and Barret battling side-by-side in a place the didn't before, or the fact that Cloud already has access to the "Summons" option of the menu in the gameplay footage? Did you see anything they missed?