Back in '08 I got the non-limited edition Season 11 DVD set new for a cheap price and it had the open side (like the S1 to 10 sets) when you just slide out the inner casing which has the discs and there's no side you have to open first to get the contents out (as seen in the following pic which i found after a quick Google search; the inner casing can be seen protruding out a bit from the side of the normal, non-limited set):
Well, today visited the local movie rental place where they also sell movies and TV series on DVD & Blu-Ray and they had all the Simpsons box sets in stock (the non-limited editions, naturally). When I took a look at the S11 sets, I saw that they now had the closed side like the S12 to 14 sets where you have to open up one of the sides first to get the inner casing with the discs out (the new side had Sideshow Mel and Bob pictured on it).
Is this a new running change or something?; It's the first time I've seen they do a change to any of the boxes so I have to say that I am a bit surprised.