A Shaymin tin would be an insta-buy for most people playing the game. Unless they already had 4 of them. TPCi would make a lot of $$ selling them. They could change the art on it so even the players who have 4 of them would still buy it. It would be a lot better than some of the boxes/tins they sell with weak promo cards in them.
Since they don't make money on Shaymin EX having a high price, they shouldn't really care if they devalue it.
PS: I never got Shaymin from the PTCGO tutorial booster pack. I don't remember what I got, but it sure wasn't Shaymin. I only got Shaymin from opening a non tradeable pack recently. Also bought 2 with some tradeable packs.
Since they don't make money on Shaymin EX having a high price, they shouldn't really care if they devalue it.
PS: I never got Shaymin from the PTCGO tutorial booster pack. I don't remember what I got, but it sure wasn't Shaymin. I only got Shaymin from opening a non tradeable pack recently. Also bought 2 with some tradeable packs.