I haven't seen the ones on Ebay but I can tell you that the style of mug (and even style of sticker) has changed since I cruised last (in January/February of this year).
My guess is that Disney will start changing the designs of the mugs and stickers more frequently as they get more and more repeat cruisers and don't want to run the risk of someone re-using an 'old' mug.
I would be careful buying something like this on Ebay as you never know if it will be the same mug design as your upcoming cruise.
My 2 cents.
John
PS The pricing of the soda program has changed on the 7-night sailing. Now it is $35.00 for the program and you get the sticker on your key to the world card. If you want the mug in addition to the sticker it is an added $3.00 charge. I do not know for sure if it is working the same way on the 3 & 4 night sailings but I will find out.