[mad=dog]

In the core rules there are two different types of decks - one with 13 cards and one with 22 - and the effects are more powerful to say the least. It is not something a DM wants to generate at random, since the outcome (which IS random) can ruin any character and the adverse effects are very very powerful mostly requiring a wish or similar to be countered.
Just to sum up some of the effects: +2 to prime requisite, 18 in charisma, imprisonment, soul strip, defeat Death (yep - beat a god...), 1d4 wishes, gain one level by defeating a monster, loose all magical items and so on.
The most radical difference is that a deck is not exhausted. Most of the cards are replaced in the deck after drawing. When all effects have been drawn the deck will disappear unless The Void (soul strip) or Donjon (imprisonment) is drawn, which will always make the deck disappear. To make matters worse there is one card (The Fool) that force you to draw again regardless of your wish to do so.
Hope this is somewhat clear. The deck is one of the oddest magical items I know of.

If they wanted to incorperate the deck in the game they should make it disappear when the game is saved to avoid scumming. That way you at least take an honest chance if you want to draw.