I just checked on Apple's support web site, and you can still download OS updates from 8.6 all the way up to 9.2.2 (with minimal searching). If you have OS 9.0.x, with a couple of downloads you can be at 9.2.2. Granted, you will want a high speed internet connection to do it, but it can be done. For OS X, the only update not available for download is 10.1.
Until we see how much has changed with 10.2, we won't know if it will be available for downloading, or only via cd. I would hope that it will be there for download as well (if you have a fast enough connection).