I seem to see this type of solution a lot with blender, and think its a bit overused. most people seem to use it to get around properly skinning and weighting verts, which I admit is a very difficult process.but autoweighting options should never be an end result, only a starting place. I wasn't planning on doing anything about weighting for a long time though quite honestly, which would give me a good chance to take a better look at the fine details of what works and why. Low poly characters though have their own pluses and minuses. perhaps the biggest issue is that you not only have to weight correctly, you need to model it correctly as well. that being said, I think I'll change gears for a tiny bit, and post a little low poly skinning modeling video. I'll be just showing the end result and theory, so it will be in max, but since there will be nothing program specific I don't think it will make a difference.
that being said. there are two things I don't like with this solution when it comes to games. 1) you are adding more nodes in your skeletal hierarchy, not sure if this is still a major issue or not anymore though. and 2) games also don't like scaling bones. so any stretchy bones should be kept to rig controls and helpers and not in the way of skinning.
that being said. here are some things that I'll go over in the video(which will be much easier to see) however I'm gonna test a couple things to see if I can get better results by moving things around a bit further.
currently the option looks like this.... bone runs down the middle of the finger(this may change if I find it works better at the top or bottom) ok, lets look at vertex placement first. your top vertex should be placed at a 45 degree angle toward the tip of the finger the bottom joint should be placed at a 45 degree angle in the opposite direction. this puts the verts in the correct place for the final pose. now as for weighting. with such minimal geometry the weighting will go 100% to the parent if you have multiple polys for the joint, you'll have most of the verts weighted to the parent bone in the joint, then you'll leave the last row 100% weighted to the child to keep thickness correct.
weighting like this should give you plenty of control for fingers without the extra bones. it will fall apart moving much past a 90degree bend, however it holds up well enough to what well enough to what the hand is actually capable of. and for the knee or elbow, you'll have a little extra geometry anyway
EDIT:Finished the video so its a little clearer what I'm talking about. http://www.youtube.com/watch?v=oWlqYGjnCEU