[kylec]

When engineering a file format, you have multiple competing priorities you need to balance, such as size of the resulting file, reading and writing efficiency, backward compatibility, etc. Since Adobe didn't anticipate using PSD as a generic file format for graphics applications, it wasn't necessary to design it that way, and I'm sure that other priorities prevailed instead. It's also a pretty old format, probably designed not just once but many times over the years by many people resulting in the inconsistencies the article talks about.