Actually when we were there last week, I was told by several disney employees that the park is almost always busy. That there's really not a "slow" time of year. That's just what they told me. They did say it's a lot busier in May, June, July & November & December.
We went last week (1st week in September) and it was still pretty busy. Lines aren't terribly long though.
Overall, yes, this is correct. However, it's also a little more complicated than just "no slow season any more."
There are definitely "slower" times, just not slower "seasons" per se. The *big* difference between DLR and WDW is that DLR is built in the middle of a city, and is largely a "locals" park, where WDW tends to be a destination park. So, WDW gets busier at larger, longer school breaks (summer, Thanksgiving breaks, winter breaks, spring breaks, etc); however, DLR gets busier anytime people aren't in school/work in that general area. So, every weekend tends to be busier, every 3-day weekend tends to be busier, etc. That being said, there's still some "slower" times... For instance, we've gone the last week in January twice, and experienced lower crowds (in comparison to July crowds). We've gone the week before "Ski Week" (President's Day is a whole week off there), and crowds were low all week, and only got bad that weekend when people were heading to the parks. Also, the annual passes play in a lot too--black-out dates play into the crowds as well, like when locals have Saturdays blocked out, or June blocked out, etc.
