I just posted in the other threategy, I'm sure they're making more cash than if they had just released one model.
Plus, why wasted all the good selling points on one phone? The Razr was the thinnest, so it sold. The Maxx was thin and had the best battery of any Smartphone, so it sold. And the Fighter will have those points plus the HD screen, so that will sell as well. But, the old models will still sell as well, as some people will decide an extra $100 isn't worth the added battery life, or HD screen.
Its a good short term strategy. But, long term, it will probably alienate some customers who are upset because they bought X phone before Y/better phone came out.