The promotion was prolonged, because Leica had a hard time to satisfy the demand. Due to the sudden "crash" of the pound in December Leica goods became cheap in UK compared to EUR/USD markets - especially with the additional rebate.
I ordered a 50 Lux in UK in December and considering the rebate, I saved around 40% compared to a purchase at my local Leica dealer. The only problem was that Leica was completely surprised by the high demand in UK, so there were delays in the shipment. I've had to wait until the end of March for my lens to be available.
This is one important reason why Leica prolonged the rebate. Since you've had to register the lens/camera in order to qualify for the promotion, they did not want to p*** off all their customers who were waiting for shipment by ending the promo as scheduled.