As long as the game that has microtransactions is a complete, solid game and the items offer no advantages over other players then I see no harm in the company that made said game offering bonus items for a price.
As for mounts costing what they do: as someone said in an above post, it costs a good bit to model, mesh and animate something. Not to mention the rigorous testing to make sure it interacts with everything in game the way it's supposed to. Now I can agree that all the items should at least be account wide for the price.
Also, as others have said: these items are purely optional. If you don't want to support them, then don't buy them. The game isn't holding your account hostage until you purchase an emote or mount.