Is DTR just the same as D which is packaged in tape and reel? If so, was it really necessary to categorize them like this?
According to the L6562 datasheet, the table you have copied is for the order codes. That's the part number you put in your order. If you want the L6562D delivered on tape and reel, then you must order the L6562DTR rather than the L6562D which is not delivered on tape and reel. The parts you receive will be marked "L6562D" rather than "L6562DTR," but they'll be delivered in tape and reel.
Yes, it makes sense to separate the order codes that way.