Why can a fish tank store have so many fish?

Glen asked:

Everyone is always talking about limiting a tank to a certian number of fish. Why is a fish shop able to safely house 100 tetras in a 15G tank, which is much more than most websites reccomend.

(As Xenical Online best as I can tell our local fish shops don't seem to be loosing tetras at at an alarming rate)

Reply:

Because they are a temporary solution - the more product they can cram into a small area, the more money they stand to make.

Because the fish store tends to do daily cleaning routines on their tanks - they keep fish as a job, we do it as a hobby.

Because you wouldn't believe the amount of losses they account for and experience. (how can you tell what they've lost?)

Never, ever look at a fish store as examples of what to do at home, not their display tanks, and most certainly not their sales tanks!