Does anyone know, or has it been stated by Bethesda that these will be released simultaneously? I sure hope not. Mounted combat is one of the best updates for me because I never, ever fast travel. I go everywhere on my horse and half the time I just run by enemies because it is more inconvenient to get off my horse to fight them. Now I'll be able to fight them on my horse, which is something I've always wanted in an Elder Scrolls game.

I have a feeling that Dawnguard won't be released until July, and I was hoping to get mounted combat long before that.

No, they have not said that these will be released simultaneously. Dawnguard will release on Xbox 360 one month before it releases on the other platforms. However, patches often release on PC first, since there is no console certification process. I expect that 1.6 will release on PC as soon as the beta test is finished and a final version is ready, and that it will then release on the consoles as soon as it is certified. I think that that will probably be before Dawnguard, unless Dawnguard comes out faster than I expect.

I'm guessing that the patch will be released before Dawnguard due to the mounted combat. The week is for any glitches that might occur on 360 that can be fixed before the DLC.