Im of the opinion that having fish in a bowl (unless it is a large bowl with substrate, live plants, and filtration) is simply a case of "fish having" but certainly not "fish keeping".
To be honest, I feel the same way about non planted (or non decorated) tanks. Fish need some kind of stimulation in their world. To this end I dont like bare bottomed tanks unless there is planty of decor for the fish to swim around and play with.
Its not just a case of providing a container to keep water in. Fish keepers maintain an environment for their fish which in my opinion should at least represent a natural habitat. Fish havers buy something watertight and dump a fish in it. If it survives they say the fish is happy - Not so! Its simply clinging onto dear life.
The linky above said (I think) that several of the livebearers died as soon as they released their fry - This means giving birth must have used their last bit of strength. Seeing as guppies in my experience can have lots of batches of fry before dying of old age - these bowl guppies cant have been healthy.