As far as I can tell, no. The only possible point is that different Pokémon learn them.
For example, Blastoise learns Protect by level up and Hitmonchan learns Detect by level up. If you don't want to waste your 1 Protect TM or have already used it, Hitmonchan must learn Detect instead. But Blastoise can always just remember the move.
Additionally, Protect will fail if used in succession, same with Detect. (in Gen 2-5) But using Protect then Detect lets you basically use Protect twice.
Is this a reason to give both to the same Pokémon? No. Is it useful? No. But it definitely is a point to Detect, even if a very, very dull one.