In general, components other than the four categories listed above are not intended to be replaceable; a few, such as processors, follow their own standards but are difficult to replace because of other factors (for example, in the case of processors cooling and access limitations can make upgrades very difficult or impossible.)
In particular, motherboards are almost always make and model-specific: locations of ports, and design and placement of internal components are not standard. Those parts are neither interchangeable with parts from other manufacturers (replaceable) nor upgradeable. If broken or damaged, they must be substituted with an exact replacement part. Those users uneducated in the relevant fields are those the most affected by incompatibilities, especially if they attempt to connect their laptops with incompatible hardware or power adapters.