There are loads of different assays laboratories use for measuring testosterone. However, most of these normal ranges are "normal" in name only.
As you can see from XMan's post, the difference between 200 and 1100ng/dl is significant, and most men on the lower end of the normal range are likely to feel at least some symptoms of deficiency, even though a level of 250 is in certain tests normal and within range.
As for therapy itself, most doctors will aim to get levels of FT in the 500-600 range citing the first example above. Besides, testosterone levels should be used in tandem with symptomology, or how the patient is feeling is on any given dose. Basically, one guy might feel great with a level of 400, while another guy might feel symptoms of low T with 400. That's why it's important to guage how the patient is feeling along with other tests like Oestriadol, and prolactin, for example.