This is pretty much standard industry practice. Take one frameset, and sell it as several different models with increasingly-better "bits" attached. Saves production costs....
You might go to your local library and check to see if they subscribe to any of several mountain-bike publications. If so, you can search through back issues for articles on fork comparisons, tire comparisons, etc.
As well, the "Mountain Bike Review" webpage has user reviews of components, whole bikes, etc. Some of the reviews are pretty poor... Like "Wow, this bike rocks!" Which doesn't tell you much. Others are well-written by fairly knowledgeable riders. Worth a look.