It is hard to argue the poplularity of a brand based on opinion, and with parks and attractions. It is even difficult when looking at actual numbers to know the popularity of a brand a few months, years, or decades down the road. What they do have is the track record of a brand.
Star Wars has been around for 35+ years. It has books, games, toys, legos (legos AREN'T TOYS!

), movies, tv shows, shirts, underwear, and every other thing you can think of. And I'm not talking about things they have had in the past, but in the past and now. 35+ years of marketing, of these being popular.
Harry Potter has had most or all of these things AT SOME POINT. Not necessarily right now. Sure, you can find them on eBay, or on the interwebs, but can you go to a store in your area and find it on the shelves (the whole global economy fight will have to go somewhere else, my point is everyday recognition). Sure, it is on the bookshelves. The movies are on tv. Overall, though, SW is out there more than HP.
HP is popular, it is still current, and it is a good brand for Universal. No doubt. SW, though, is that and more. It will be interesting to see if that picture of the WWoHP line stays the same when the new section opens. I would not be surprised if it is. Why would HP get that kind of attention and not a Disney land opening? Personally I think it is the crowd that each park attracts.
My sister is a long time Orlandoian with three children. She moved down to Orlando when they were in elementary school and younger. They would go to the Disney parks with the rest of the family when we would visit, when she could. As her kids got older they found Sea World a better fit for them, partly based on money, I'm sure. In their teen years they matured as Universal did. IoA opened and that is all they would do for years and years. Disney, BORING! Now, however, her two eldest are parents of their own. Where do they go? Boring old Disney. Why? Their kids.
That is not to say that everyone finds Disney boring, or Universal exciting, or any other variation. Some people just like one more than the other. Those that have done all of the parks I have found like all of the parks. Time, money, and family will dictate which they visit on their trips more than anything, though.
I have a six year old, and a teen as of tomorrow (birthday!). We go to WDW once, twice, even three times a year. We went to Sea World last year, and will go again in a few weeks on our 'Disney' trip. Next year we will probably go to LegoLand on our 'Disney' trip. When the youngest can ride most of the coasters at IoA, we'll go to Universal, and I'll be happy to take them. BUT! It will be on our 'Disney' trip.