Tomb Raider: Anniversary only available in Collection?

I want to buy Tomb Raider: Anniversary only, but it is not possible? On the store page of the game is no "buy" button. Only the link to the complete collection (which I don't want). Is this a bug? Anyone else with the same problem?

EDIT: So it seems to work in some stores, but not in all... then probably the 91% discount is really a price bug.
For me everything is 91%, Legend and the new one are 75% and as I said Anniversary not available at all.

EDIT2: Using the "trick" described here worked fine for me :)

EDIT3: Note that the "trick" above is NOT violating the ToS of steam and completely legal! You don't have to use a VPN and in the end you will pay in your own currency. The trick is just a way to fix the missing buy button on the store page of Tomb Raider Anniversary. For reference I will repeat the steps here:

1. Goto to http://store.steampowered.com/?cc=US
2. You are now using the US-Steam-Store (thats why all prices are displayed in $)
3. Navigate to Tomb Raider Anniversary or just use this link
4. Press the wonderful "Add To Cart" button which is now magically there :D
5. Checkout
6. Use paypal as payment method (confirmed to work), Steam Wallet DOES NOT WORK!
7. When trying to continue, Steam will notify you, that the selected payment method (your country) does not match with the used store (US store) and will automatically UPDATE your cart with the correct currency (but it will NOT remove Tomb Raider).
8. OPTIONAL: As your cart is now updated, you can probably change your payment method now to whatever you prefer (including steam wallet)
9. Just continue with the payment as usual!