Actually, it simply isn't the case. The same number of restaurants that were participating in the Dining Plan earlier in the year are participating in the Dining Plan right now. There hasn't been any "slashing."
What you may have heard is that the first version of the 2007 Dining Plan brochure doesn't include any of the non-Disney-owned restaurants. The most likely reason for that is that 2007 is over four months away, and so contracts for 2007 aren't signed yet. While it is likely that a couple of restaurants will opt-out of the promotion, we can probably count on the vast majority to remain participating and guests should notice only minor changes between this year and next, once next year's plan is solidified.