I would also argue, though, that both DL and DCA close early during off season (as early as 6pm) and that neither park has evening EMH any time of the year, including during the holidays. So opening at 7am makes more sense -- Disney is going to get more guests who want to get up early and get on (and off) the 5 before the real traffic starts; they don't have nearly the number of onsite guests WDW has. Plus ... there are only a couple of fine dining experiences throughout DL and DCA -- most of the
Disneyland restaurants are in the resorts or DTD.
WDW, on the other hand, has a lot more people staying onsite, and Disney wants those folks to eat at the resort character breakfasts, go golfing, etc., and that's easier to do without a 7am pull to be at the parks. Additionally, WDW stays open far later -- MK as late as 3am with EMH -- so WDW guests are more conditioned to stay up late to avoid the heat than to get up early. You want to get up early and see Epcot in the daytime before the heat. Disney wants you to take your midday break and then come back to Epcot in the evening to dine in one of the many restaurants in that park. It's just a different strategy.