Regarding "real" concrete. Real concrete can mean a lot of different things.... but one thing I notice is that concrete laid before the early 20th century kind-of breaks apart and corrodes, whereas after that, it becomes much more durable. This may be in part due to better formulations but the main reason is that "old-school" concrete often did not have the magical ingredient of rebar. I'm sure all the gory details are on Wikipedia
Without consulting Wikipedia, I know that when I was a child, even though my house was on a concrete slab, weeds and stuff would break through it. Clearly the elements were attacking that slab, whereas, nowadays, only super old or super cheap concrete surfaces seem to work that way. Maybe also today stuff gets scrapped so quickly it never reaches that state of decay -- but honestly I think it's mostly the ubiquity of rebar and availability of cheap pig-iron that drives this. Point being, it's not totally crazy to imagine there might be more than one kind of concrete, one that's "immortal" and one with more of a run-down"dieselpunk" quality (I do think the pictures look nice fwiw).
However, I think from a gameplay/functional standpoint, "paving the world" is a late-game activity. If you know what you're doing, you know that all that concrete is increasing your pollution radius and contributing to your death-world problems and maybe even adding lag. That's all fine, I guess.... my point is, if you are laying down concrete as a replacement-terrain (ie: if there's concrete underneath your solar panels

) that's a very different thing than, say, building walkways or even building a 10-tile-wide two-lane "super-highway" for you and your buddies to drive on.
Once you've reached the pave-the-world stage, I kind of feel like you've gotten your requisite eyeful of dieselpunk and are probably focusing on some other thing: maybe you want ice-cold aesthetic uniformity (that's usually my motivation if I do this) or you want to be able to get around as fast as possible on foot, or ... whatever. Doesn't matter why, just matters that, there's already a built-in cost and hopefully, you can afford it. If so, you've probably got 10 or 100 rockets in the air, invested hundreds of man hours, the game is "won" ... basically, you've earned the right to run around with a bag full of nukes doing more-or-less doing whatever the hell you want, and constraints like "well there's no smooth terrain in available in factorio, it's not consistent with the aesthetic we're trying to create...." start to seem a bit constraining.