> We pretend but flexible viewport size is not actually possible.

Not beyond a point, but it's still very useful to be flexible up to that. For example, I'm very grateful that a web page will reflow text rather than print everything on one line and force horizontal scrolling.

Yet, for some reason, mobile browsers do not reflow when you zoom in, but instead insist on horizontal scrolling, unlike their desktop counterparts. I've never understood that.

It is not like we have a choice. I forgot to mention that people also have different eye sight which further complicates things. Some set the font so large half the apps fail to fit. Before many people had one I see someone browse using an enormous TV with very high resolution. The google adds sidebar lived on the other side of the room. % size images upscaled into a pizza of artifacts. There wasn't a website that looked the way intended. A funny I ran into once was Lubuntu system dialogs with the accept button below the screen. I've also seen enough print previews where one cant read the text. The use of colors with poor contrast only on some displays.

We are having a lot of fun pretending it is possible.