Earlier versions of Photoshop (CS5 and earlier) does not come with ACR. You have to add it...if you don't or don't care to, that just means you are using something else. Just because someone says they use Photoshop, that doesn't necessarily mean they use ACR for their RAW files.
I disagree, I've been using Photoshop since Photoshop CS1 and it always work with my raw files (shot with the Canon 20D and 30D). Yes sometimes it might not work because your Adobe Camera Raw plug-in is outdated and doesn't support the latest cameras but all you need to do is go and download the latest camera raw plug-in. Camera Raw was first introduced and came natively with CS1.
The only difference with earlier versions of Creative Suite was that you had to manually update the camera raw plug-in unlike later in CS4 where the Adobe Software Manager automatically notified you of updates.
Also if you didn't have the ACR plug-in, you can't even open a camera raw file in PS, Photoshop will indicated that it's an unknown file so the only way to be able to open a camera raw file in PS in the first place is by having the plug in.