It is also important to remember that any selections from the fish store will represent only a sample of the population. So, while as a species, a certain fish may be calm and suitable for a community tank, certain individuals can be aggressive or bothersome. Similarly, a species may be hardy, but certain individuals from a sample of the population can be less hardy.
Secondly, the species themselves have been changing. The neon tetra, once considered tempramental like the cardinal, has now been coaxed into breeding in the hard, alkaline waters of Flordia. Consequently, most neons in the stores, mass produced as they are, are very tolerant of a wide range of water chemistry. A book with older info may not reflect this.
And lastly, even the experts themselves do not always agree on things. This kind of goes back to my first point, but more so that different scientists will study different parts of a populations, possibly in a different geographice location. And if you think that the differences should be simple to determine, just look at how often the scientific names of the species change, as scientists change their minds on which family etc. an individual species belongs to. So, even the full-time scientists do not agree.
Ultimately, this is why you have to be able to make up your own mind after wading through all the different expereinces by posters here, books, magazine articles, LFS employees, etc.