You're right in that everyone is different...however, my ortho, who generally was not too helpful, did say that walking 'religously' was very important if I was to avoid surgery. The PT that I visited soon after being diagnosed with two herniated discs, said I should get to a point where I was walking 2-3 miles per day.
At this point, I try to walk about 2-2.25 miles, 4-5 times a week. I also try to do a routine of stretches and strengthening exercises. It's tough to do all that every day, because it's pretty time consuming. My suggestion on the treadmill is to work your way up to 2 miles or more, which takes around 30-40 minutes of walking. Also, remember to have good form when you're walking, stand straight, and tighten your abs the whole time, to get maximum effect. I have this big ice pack that I generally apply for 15 minutes afterwards...and that also helps. Good luck, and don't overdo it in the beginning.
Keith, your disc does not have a blood flow. I think the idea is to increase blood flow to the surounding tissue to help it absorb any disc material that has broken off the disc. It also strengthens your back muscles taking stress off of your spine hopefully helping with a bulging disc.
As far as walking, I would walk as much as you are capable of without causing too much pain. The pain should be your guide. If you walk too much and feel bad afterward, it will make you not want to walk. Do what you can to start and try to increase it when you can tolerate it.
I am going to keep walking a part of my life for the rest of my life. It is good for my back and my heart.
The only benefit that I know of is strengthening of the back and ab muscles, and generally strengthening and stretching leg and other muscles. Generally speaking, my understanding is that all this exercise and stretching strengthens muscles which helps to align the spine better and support the natural curvature, etc...one of my PT's made it sound like it takes pressure off the discs by supporting the spine. Sounds confusing, but she had the model of the spine, and was very convincing.
As far as the '2 miles a day for life'...it kind of sucks, doesn't it? I think from time to time how nice it would be if i had a healthy back. How i would be careful, and have good posture, and exercise in order to avoid this. But you just have to be optimistic and do what you have to do, in order to try and have a normal life. Besides, like AlSmith said, walking is good for you in other ways too...so there may be a silver lining in all of this. Sorry to ramble..good luck with the treadmill.