Ah, but this is a different situation. They appear to be offering suggestions to RETAILERS, who receive bags of fish with sometimes 50 or more individuals in it (eg in freshwater) and some fish that may have been in the bags for 10 or more hours during transport. Their logic is that the fish are very stressed, they are in water with a low pH and high ammonia (because of the exceedingly high number of fish in the bag and/or duration of transport). In this case, it is considered better to briefly temperature acclimate (in most cases 10-15 minutes) and then dump the fish in (pour them through a net and discard water).
The reason for this is that at lower pH (which the shipping water will be due to the fish prodiving CO2 which combines with water forming carbonic acid and dropping pH) ammonia is less toxic...and there will be lots of ammonia. So if you drip acclimate, you raise the pH, and the high levels of ammonia suddenly become quite toxic, resulting in rapid fish loss.
Betta fish, for example, come packed from Asia in tiny bags with perhaps a tablespoon of water in it (and it is mighty nasty)...getting them out of that seems far less stressful than leaving them in for any minute longer than necessary.
But, you missed where they suggest fish be kept in a Q tank for 7-10 days before selling? This is to allow the weak one's to die, and any stress related diseases to settle or become apparent before selling the fish. Now if an LFS losed a dozen fish out of 50, what the hey...it is different for you, no?
IMO, this has NOTHING to do with acclimation of fish at home, where the animal has been in a bag maybe an hour or two at most, with very minimal pH drop or ammonia production. Totally different scenario. The above issues no longer come into play, and therefore, the major stress comes from the risk of salinity, temperature or pH shock simply from differences between the LFS and your tank.
I would follow Bang Guy's advice on this.
Q tanks are also helpful because they allow fish to settle in without having to fight with established fish. It also allows you to deal with any diseases that are commonly contracted by fish in transport through an LFS.