They used a cast flange on the new one to save time and therefor money on production. Maybe they didn't think the sales volume would be as large as it is now and didn't invest their money into making the cast. It must have taken a lot of man hours to make the old ones (if you saw the craftsmanship that had to go into the old flange).
It also looks like they added a capped bung near the flange side for a wide-band sensor? I'm not up to par on gauges, so someone else can chime in there with a confirmation.
