Yeah, they just changed connector suppliers somewhere along the line. They do that from time to time. Can't get supplier A to provide enough on time for production, supplier B out bid supplier A, etc.
But rest assured the slots are the same performance-wise. The only difference is the locking tab mechanism at the end of the slot. The slots' locking mechanism in the pic on their web page flip up automatically to secure the card in the slot. You have to remember to press down on the lever(s) to release the card for removal. The ones in your pic use a lever you manually slide to lock the rear of the card. Slide back to unlock it. Go ahead and give it a try, you'll see what I mean. I actually prefer the ones in your pic better.