The fact of the matter is, as pointed out in other threads, things like these really aren't exact sciences. Neither is how long a fish will really grow/min. size tank. Ask, and you'll typically get different answers. (Liveaquaria.com says Otos should be in a 30g minimum, yet many others say they do fine in smaller tanks.)
Also, fish do have their own personalities. The Betta we had with 3 Gouramis never seemed to even notice them. Some people succeed with a Neon Tetra/Betta/Shrimp combo, some Bettas eat the shrimp/Tetras, some Tetras nip the Betta's fins. If anything, charts like that should be a rough guideline...
The charts also don't tend to take into consideration the size of the tank/territory and room, and genders of the species.
It's probably best to gather as many real tank scenarios as possible, but in the end, you may still end up with a different result... /shrug
But yeah, charts and things like that are definitely guidelines and not hard and fast rules. (Then again, they are highly educated/degreed veterinarians, so IMO they have a slight leg up.)