Display issues at lower Resoultions

Hello,

So my question is this… Over the years of using wordpress to build websites I notice that at lower resolutions or when zoomed in the site tends to distort. The “Distortion” is different for each site:

menu shifts from one line to two lines
Sidebars overlap onto the main content area
in extreme cases the site totally explodes (everything just scrambles)(I don’t see much of this anymore).

Each site varies in what distorts. There are some that don’t do it at all. This issue isn’t browser specific and I do have some sites that are exempt from this issue.

So my question is: I’m I correct in assuming that these issues are because of the theme?

I know this is kind of broad but it seems too common to be simply a plugin conflict.