Not surprising given the vast number of titles they put out. It's like everything that ever came out in the cinema or on TV is now available on DVD. It's like when CDs took off - everyone replaced their old vinyl collections and the record companies made a mint re-releasing their back catalogue. Then when everyone got what they wanted, sales slowed down and the the entertainment cartels started crying about piracy because they no longer had this "new adopter" blip in the market to make them money for nothing.
At the same time the price of a DVD is quite expensive for newer movies, at a time when a lot of people are feeling the economic pinch, maybe saving up for one of the new consoles or even looking towards HDDVD and Blu-ray for their new collections, etc. A slow down is inevitable - the market ensures it by obseleting equipment in order to sell new stuff to people - they just don't like it when the customer does the same thing back and loses interest in a market because it's no longer new and faddish.
