That's not at all true. In addition to the lack of variation in stride that gaius points out, it's almost impossible to not cheat on a treadmill and let it do

That's not at all true. In addition to the lack of variation in stride that gaius points out, it's almost impossible to not cheat on a treadmill and let it do some of the work for you, and there's no wind resistance. Treadmills have their place - for warming up a bit before some other kind of exercise, or as a replacement when the weather or traveling keeps you indoors - but they just aren't equivalent to real running. 5 minutes on a trail will tell you that.