A manual isn't particularly useful on its own, since it's full of implementation details for one particular widget. SPJ is emphasising that details and descriptions of implementations should be avoided in favour of ideas and intuitions.
A purely theoretical paper can still be useful. It's even more useful if it's followed up by an experimental paper demonstrating or refuting the idea.
For example, it's silly to write a manual "How to use Google", then make Google. It's very sensible to write a paper "A proposal for improving Web search with mutual-popularity measures", then try to make Google. If Google succeeds, we can write "Mutual-popularity measures and Web search: large-scale experimental results". If it fails, we can write "Scaling issues on the Web: impacts on mutual-popularity algorithms".
Comments
A manual isn't particularly useful on its own, since it's full of implementation details for one particular widget. SPJ is emphasising that details and descriptions of implementations should be avoided in favour of ideas and intuitions.
A purely theoretical paper can still be useful. It's even more useful if it's followed up by an experimental paper demonstrating or refuting the idea.
For example, it's silly to write a manual "How to use Google", then make Google. It's very sensible to write a paper "A proposal for improving Web search with mutual-popularity measures", then try to make Google. If Google succeeds, we can write "Mutual-popularity measures and Web search: large-scale experimental results". If it fails, we can write "Scaling issues on the Web: impacts on mutual-popularity algorithms".
It would indeed be silly, since Google is not a program.
Google’s search engine, however, is, and it would be perfectly sensible to first write a manual for a search engine before implementing it.