Yes, you are correct. The srh750djs were designed from the ground up with djs in mind, the hd25s were not. That didn't stop them from becoming popular with the dj community though. The fact that parts were replaceable helped to make them popular. It wasn't until after then, that sennheiser started pushing the hd25s with the dj angle. I don't even think my packaging for the senns even mention djing. This is evidenced by the swiveling, and flipping earcups on the shures that some djs like. The hd25 has one rotating earcup on the left side. They both have replaceable cables. I imagine parts would be much easier to replace on the hd25. I have both cans and think they're both great. I'm not a dj, but if I were to pick one for djing, it would be the hd25. imho, it wins on durability and portability. Comfort would be a toss up. I also like their more understated and utilitarian design. I prefer the sound from the srh750djs though. For isolation, the graphs on HeadRoom matched my observations closely. Their difference in cable design and length might be another thing for a dj to consider.
If your serious about buying dj headphones and just getting started on your search, I wouldn't just get fixated on these so soon. Have you read this group test on scratchworx?
http://www.skratchworx.com/news3/comments.php?id=1487 I read it and I'll just say that I thought it was interesting.
You might also be interested in the skullcandy mix master's and beats pro headphones (was called the dj spin). Both are out of your price range but might fall within it after some time. Both as far as I know haven't formally been released yet. Both appear to be designed with djs in mind.
Regarding the 750djs and the hd25s, I have pics of them side by side in my album. I had a review in my headfi blog for the 750djs, but it disappeared when headfi changed it's format. Anyway, good luck with your search and welcome to headfi.