It's close to that, Mcgyver, but not quite so catastrophic. What I mean is there is useful torque at greater than 0 rpm, but it falls off quickly. You can get the torque curves for them. Here is one such example:
http://www.kelinginc.net/KL23H276-30-8AT.pdf
A typical stepper is 200 steps per revolution. That chart shows half steps, so we'll say 400 half steps per revolution. Now let's take a 1700 rpm motor (forget 3400!). On that chart we're at:
(1700 rpm / 60 secs/min) = 28.3 revs/sec * 400 steps/rev = 11,333 pulses per second
Referring to our chart we're at circa 0.3/1.5 Nm = 20% of peak holding torque. Bummer!
Of course our regular motors lose torque rapidly (without a vector drive or other aid) when we slow them down so we have the reverse problem.
The solution to the regular motor problem is some form of gear train: step pulleys, gear box or whatever. The same will work with a stepper. Can you achieve acceptible performance in the rpm range you require? Perhaps.
Why would you care? Well, at the risk of continuing to be long winded, it's pretty handy to be able to index or otherwise precisely control your spindle speed electronically. At the low end, this is handy for threading, for example, where you can thread with an electronic gear box. But that's easier done in other ways. See for example the Electronic Leadscrew Yahoo Group (started by a crazy discussion I launched on a lot of boards a long time ago, but you can actually buy/build one and it's cool).
Alternatively, if you are into CNC, as I am, it is pretty cool. If I can index the spindle under CNC control, I can stick my chuck with an air spindle on the cross slide, but a drill bit in it, and drill a bolt circle in the lathe as part of making a part.
Hmmm. But how do I get the best of multiple worlds?
Well, I can use 2 motors. I can use a regular motor for turning, and a second stepper to index the spindle. I may want to use a disc brake to lock the spindle while indexing as well. Similar things can be done to automate rotary tables and indexers too, for example.
How do the big boys do it? It's quite common (almost mandatory in fact) to use a very large servo to drive your spindle. I've mentioned at least one cool thing that CNC lathes do with that (bolt circles) and there are many more. Another is polygonal turning. If you've never seen that, it is mind boggling. If we rotate a cutter in precise synchrony to the spindle on the lathe, we can "turn" polygons. I can make round stock into a hexagon, for example. Sorta like a rotary broach, but different. Pure vodoo magic!
Here is an animation of polygon turning:
http://video.google.com/videoplay?docid=-7831550688320827327
As you can see, synchronization is essential!
Mills do cool things with it too. Thread milling is one, where the spinning cutter follows a spiral path just right to cut thread, just like on a lathe. On a simpler vein, most CNC tapers have "ears" on the taper. When the tool changer engages, the spindle has to index the ears or the toolholder won't go in the spindle. Having the spindle itself as a servo that you can index to any desired position is a happy thing.
So, being able to control more about a spindle motor than just it's speed is a good thing. In other words, precisely controling its position at all times. Steppers can do this, but they don't produce much power at very high rpm. But, we can also do this with servos for a little more money. And yes, it would be valuable to understand that rotational position on a hard drive too.
So there you have it. Much more than you cared to hear on the topic, I am sure.
Cheers,
BW