Gentlemen, I do believe that they will either be servicing the servers, or installing a new patch. I recently have found that several servers have gone down, and accompanied by a red message indicating so, in the attachment. This could either be a ladder reset, patch, or servicing.
I'll bring you more information once I know what is going on.
Read this for LoD patch history. There is also a "problems fixed" patch batch in your DII folders in the guise of a notepad file. In case you are too lazy, I have uploaded it for convenience.
If it is servicing, then it's because of WoW. Simple as that.
Ladder Reset, then a middle-level RustStorm will be run, deleting most duped, non-changed ID items deleted, and characters and items moved to the normal Realms.
If it is a new patch, then it will require both of the above, the first patch since 2005.