I've been noticing something strange with browsers and displays in W10

Greetings.

I have noticed on all systems running W10 (any flavor) that certain windows applications and browsers that are not maximized, an inability to be stretched all the way to the screen edge as in W7.
This only appears in landscape (horizontal) mode. There is about 3 mm total gap size (1.5 mm) on each side of the display where you can center the window but it won't stretch the full amount.

Am I seeing things? If not, what might be the cause?

Again, I have seen this on many different W10 hardware configurations.

Thanks.

Do you have 3 icons in the top right corner of their window? The left or - is to minimize, right is X to close and the middle one will be either a square or stacked squares. The single is to Maximize [not to be confused with Full Screen] and the stacked is to Restore Down [or the previous view]. Do they function correctly? I have seen programs set their screen as desired, one that comes to mind is Roxio's Easy CD Creator, doesn't shrink down enough.

Also, what is the screen resolution? Is it set to the recommended size. Do things that are supposed to be round actually are or are they slightly oval?

@Berton -

Yes, I am somewhat familiar with those three symbols, lol.

My observation is at the native resolution of the monitor or one with a matching widescreen ratio. On this system right now, it's 1080p, which is 1920x1080.
On another, it's 2560x1440. Monitor geometry is totally accurate. Question would be the accuracy of the color profile (file) from the manufacturer.

Well, it's been about 150 views...

Guess I have to claim insanity!

Seems right to the edge on mine- e.g. file explorer, not maximised- max window width = 100% screen width...