There is good post by Ken Druse at Garden Rant concerning the use of peat moss. The concern over peat bog depletion is the crux of the post with reference made about peat substitutes like coir. The post also addresses Monrovia's foray into potting soils. The following is the comment I left at the post. We carry coir as a substitute for peat moss. Peat still outsells coir, either because people like what peat does for their potting soil, or they don't know about coir. Peat is generally acid reacting so it's great for acid loving plants like blueberries or azaleas. Coir is neutral, and I have had a couple of people tell me that is why they like coir. No one in our area uses peat moss as a soil conditioner. It's use is almost always for seed starting, and container mixes.
Monrovia's website focuses on what they think is important in their "soil". The ingredients for all soils are listed on the bag, from the most used to the least. Peat moss is there, just like most quality potting soils. The lack in mentioning peat in their website is not unusual in the potting soil world.
Many people focus on the cost of the product rather than what's in it. When people question the price of an exceptional potting soil I use the ingredient list to show why it's better. Just like Monrovia's website say's, "If your mix contains too much sawdust or fresh bark, for instance, you will likely see the leaves of your plants yellowing due to a nitrogen deficiency." That's what makes up the majority of ingredients in many of the cheaper potting soils, sawdust.
So if we are concerned with the depletion of resources, what about the sawdust that is used in many potting soils, and bulk purchased soils? It's use is far more widespread than peat.
Just as you point out that, "Some wetlands scientists point out that a managed bog lacks the biodiversity of the original bog", so the forest where the sawdust originally comes from also lacks that "biodiversity" of the original forest. I also wonder about the coconut plantations where coir is harvested from. Are they bio-diverse? Coir comes from fibers found between the husk and the outer shell of a coconut. The coconut plantation certainly displaced the native flora and fauna of the area they are grown in.
You are correct that compost makes a great soil conditioner, though people growing in containers generally need a potting soil, not compost. Some will make their own, but most buy the bag, and either way they use many of the same ingredients.
I am stunned that the manager of that garden center did not know where peat came from. This might explain why peat moss is used so often where is shouldn't be, in the ground. Perhaps through education we will be able to steer people to better alternatives for their situation, and thus avoid the depletion of the peat bogs. It's not the use of peat that is bad. It's the misuse of peat in situations where it is unwarranted that causes problems.