Doug has pretty much taken the words out of my mouth... thorough flushing is the important bit, but they don't tell you that on the label of products, or at a basic CC course.
For the last couple of years, since changing my extraction machinery (carefully avoiding the same old debate again here!) I've found that I can pull 2 or 3 times the amount of water through a carpet and leave it just as dry if not drier. If you remove the product, it can't cause a problem! The acid rinse is just a bit of an insurance policy in my opinion, and should be treated as such.
I regularly use powerburst, ultrapac, HD microsplitter etc on wool... gotta use the right product for the job in hand! Don't forget as well that a lot of soils are acidic in nature, therefore partly cancelling out the alkalinity of the pre-spray