It's been said several times that the July release is not about making more money out of it. That's unlikely to work anyway.
The reason for delaying it is EITHER
- because it really isn't very good, and despite the claims that it's finished, they have realised that it neeRAB a lot more work to avoid sinking the whole franchise; OR
- simply because shareholders/investors really don't get on well with ANY company that has very changeable profit/loss from year to year, so by pushing this into the next financial year they maintain a healthy and similar profit level each year (batman this year, potter next year) which keeps the financial analysts a lot happier than a huge profit this year with two blockbusters and then nothing much in the next financial year. I used to work for an oil company that quietly bought (some years) and sold (other years) loaRAB of Mayfair property (didn't actually do anything with them) purely because it was a very effective way to quickly "get rid of" a few hundred million pounRAB spare cash one year and get it back into the books the next, all so as to engineer the year on year profit to be a steady few percent and make the bulk of the shareholders think the board were really in control (you would have had to look into things really deeply to realise what property was concerned and that those properties just sat there doing nothing).
It's really quite strange to leave it this late in the schedule to make this call on a financial accounts basis, aside from all the marketing and toy suppliers/retailers etc that will now be furious at their trashed Christmas sales and so will likely not trust Warner release schedules again, the whole World Premiere was already set up, with tickets and advertising in the programme all sold already. I would have thought that, although the financial reason makes a lot of sense (as I've explained above), if that were truly the reason they could have made that call weeks ago when Batman had it's opening weekend and possibly even earlier. So personally I favour my first reason - that the film is really not very good at all, so bad in fact that the whole franchise could be hurt. I would put money on the fact that we will shortly hear that "they have decided to take the opportunity to reshoot some scenes" making out that they're just taking advantage of the delay for any reshoots or re-edits rather than admit the reshoots/re-edits are the cause of the delay.
Yup I work in the film industry and the people I've talked to reckon keeping control of it is going to be a HUGE problem. If it is indeed finished and not a piece of junk needing lots more post production to clean it up they are going to have their work cut out to avoid it leaking for so long. Some guys I know are still doing sound mixes for a big name film that's out in about three weeks, that's how close to release it often is before a film is complete and versions exist that are worth pirating.
All over! 
pictures, the fourth picture with the mirror of erased and the second from last! Gutting 