Unfortunately, your assumption is wrong. Sorry. Inkscape is not just a vector image editor, it's an SVG editor. SVGs are a kind of XML, basically just code.
Some SVG shapes are not actually paths - they're SVG elements like this:
<rect x="21.1" y="54.6" width="34.3" height="18.6"/>
<circle cx="38.2" cy="103" r="12.9"/>
<ellipse cx="38.2" cy="142" rx="16.4" ry="7.5"/>
As you already said, you can of course turn these into paths if you want. In Inkscape select a shape and do Path > Object to Path. This will convert the shapes into actual vector paths, something like this:
<path
id="rect846"
d="m 21.061296,54.616585 h 34.26923 v 18.5625 h -34.26923 z" />
<path
id="path870"
d="M 51.046873,103.16467 A 12.850962,12.850962 0 0 1 38.195911,116.01563 12.850962,12.850962 0 0 1 25.34495,103.16467 12.850962,12.850962 0 0 1 38.195911,90.313711 12.850962,12.850962 0 0 1 51.046873,103.16467 Z" />
<path
id="path872"
d="m 54.616585,141.71754 a 16.420673,7.4963942 0 0 1 -16.420674,7.4964 16.420673,7.4963942 0 0 1 -16.420673,-7.4964 16.420673,7.4963942 0 0 1 16.420673,-7.49639 16.420673,7.4963942 0 0 1 16.420674,7.49639 z" />
As you can see, there are situations where an SVG element is preferrable. It can for example help reduce the file size of SVGs, also SVG elements are editable in the sense that you can easily change their parameters, something that's not so easy if you just have paths.
There are also other benefits to leaving shapes as shapes in Inkscape rather than converting to paths. Circles can be edited as segments, and polygons and stars can be adjusted with controls, and rectangles have adjustable curved corners, etc. If you convert these to paths, these functions are no longer possible.
Example
