Kenny Perry's not too old, but he certainly keeps the foot down through Impact. I often use something in my teaching to demonstrate this very point.
I have no issue with the segments slowing and transferring momentum to the next segment. It's the intent that I question. Do they slow? Yes. Can the intent to "brake" increase speed? I highly doubt it.
With the 3-D machines I can find out if a flat foot pivot or trying to brake the hips will add club head speed and if so can a golfer learn to do it. I am going to check it out. Here is a slow motion video of Tiger keeping the right foot down through impact.