So I know Dawnguard will add a load of new features, and what I'm wandering is whether there'll be an update released at the same time, that allows players access to horse combat (and other features that couldn't be justified as exclusive to Dawnguard), if they don't download Dawnguard... won't be a problem for me, I'm just asking for the sake of others.

The update is out for the Xbox and the PC is in Beta.

As Cinco stated,

the update 1.6 already contains Mounted Combat, it only isn't out yet for PS3 and PC. Once it officialy comes out, you'll know.

Yeah, got the update yesterday... I'm on Xbox

What? You don't need dawnguard for horse combat...

That's correct, it's included in patch 1.6 for everyone.

And it's out of beta for PC users. Not sure when it will roll out for PS3, but I would imagine it should be soon.