As others have said, I got caught out with my old Canon 350D. I was happily using my Adobe software to process and work on images and then CS4 came out without RAW support for the older camera. I then had another step in my workflow with Adobe Camera Raw. It's just easier to convert to DNG on import. You've then got a format that's widely supported.
As far as I am aware, Adobe haven't stopped supporting any RAW formats.
The version of the Camera Raw plugin that came out with CS4, ver 5.2,
lists the Canon 350D as one of the supported cameras. That is why the Camera Raw update got bigger as more cameras were added, but no formats were forgotten, plus they added things like the camera/lens profiles. I think the last time I downloaded one separately, it was over 100mb.
The ver 2.4 update was 1.6mb.
People cite not being able to access their RAW files in the future as a reason for converting to DNG. There are millions of people using these various RAW formats, and the code to read the files has already been created, so I doubt a file will ever become unreadable. And the Adobe DNG converter can be used to convert to DNG in the future. And if the Adobe software can convert them, then the Adobe software should be able to read them.
So why not just convert anyway? It takes time, if you are in a hurry to process files. As the argument goes that you don't have to process every RAW file, just the ones you intend to make into pictures, you don't also have to convert every RAW file DNG, as you will again, not be processing every file, so why convert them all!
I know some Pro's convert RAW files to DNGs for archiving for the reasons above, but that is after the keepers have been kept, and the rest deleted. And processing has been completed.
I'm no Pro, but I like having the original files available, and I have my files organised so as they don't have to be moved. And if they are, for a new HD for example, it's folders with RAW and associated XMP sidecar files all being moved together. I also use Adobe Bridge and Camera Raw, and so I can open a RAW file as soon as it is in the computer.
In the past the Nikon software could process the files better than Adobe, (not sure about the new Nikon software) and some people swear by the Canon software for processing too. I couldn't get on with the Nikon and Canon software, and like the UI and extra processing options of the Adobe software more.