To respond specifically to this post -- and not to "take sides" -- I don't think that Disney is trying to recoup their cost during the specific hour that it's open to the little ones. Rather, as others have posted, this is an extremely slow time of year for Disney. They can't effectively market to families with older children, since most of them will have just started school and likely wouldn't be coming to the World. Likewise college students. Adults already, ostensibly, have the freedom to vacation when they want to (and please, no one correct me about how you have to vacation at certain times of the year -- I'm speaking in generalities), and Disney is enticing them with Free Dining. So, if I own a theme park and have a couple months downtime, what do I do? I find a demographic that might be underrepresented and try to convince them that they'll have a great time if they come. A lot of people don't think that smal children will enjoy/benefit/remember, etc. WDW. Even the Unofficial Guide says not to take them if they're under 7 (naturally, I don't agree!). So, if I get these parents to come to WDW, stay at a WDW hotel, buy WDW souveniers. . . I'm going to make more money.
My point is that Disney is a big corporation, and they're trying to find a way increase attendence by appealing to groups who might not normally come. I would think the younger age limit is an acknowledgement that there are fewer rides these little ones can go on, and making those rides more available could help a family decide to take little Timmy or Susie now instead of waiting until they're 10 and can ride pretty much anything they want. And if I'm Disney, I want to get those families hooked on my theme parks as soon as possible. Besides, as one heartless poster put it, it's only 1 hour a day, three days a week, for a limited time, so who does it really hurt?