I think the waiting post-partum waiting period will completely depend on your own situation; there can't be a uniform guideline for everyone. The nature of the birth itself will impact how long it will take for you to heal, and your own prioritizing will also determine when you are ready to start again. The birth of my first daughter required a lot of healing for me, and I had no desire to do anything even slightly strenuous for a couple of months. I felt like my insides were going to fall out from the slightest impact! Not everyone has this kind of experience, though.
I'm not sure why doctors recommend waiting 6 weeks post-partum to resume exercise, if the birth was a "normal" experience. I know that it takes 6 weeks for the cervix to close again, so maybe it is related to that? Is there some kind of risk associated with exercising with an open cervix? I don't know.
Certainly there are different levels of exercise, and accommodations can be made to match the intensity level with the post-partum healing stage.
In the first few weeks post-partum, our bodies go through substantial hormonal changes, more dramatic than the first trimester of the pregnancy. You can't predict how these changes are going to make you feel, so you might find yourself completely unmotivated to exercise, despite all your good intentions. I think it's great to have a plan in place for resuming exercise post-partum, but to remain open to the possibility that you may genuinely want a few weeks away from it, and not to beat yourself up about it. In the long term, it won't matter whether you resume your exercise program the day after delivery, or 3 months after. Just make sure that whatever you do, you do your best to *enjoy* those first few weeks with your newborn! It is a rare and precious time, unlike any other phase of your child's life.
Cathe herself took a full 7 weeks off from exercise after the birth of her second baby, and it doesn't appear to have done her any harm. Ultimately it's a personal decision, based on our own circumstances.
Cheers,
Sandra