Most nurseries want to make money, i.e. make the plants grow and bloom fast. That is why they are rather cheap to buy for us. Repotting (and removing old medium) would set the plants back, so they usually don't do it. That's why you find those sphagnum or foam plugs. They just take it out of the pot, put it in a larger one and add medium.
It's hard to say what those bugs were. Maybe try comparing them to pics online?
Pest Control Library: Bug Mugs - Garden.org