If you look at XP, you have SP1, SP2, plus over 100 mb of other patches. Looks like a good case for more frequent updates, or at least, refresh copies of the basic media.
It's true that there are many, many updates to apply if you're installing XP now. If it's been installed for a while, though, the updates are no big deal because we've been applying them all along. Microsoft did issue a Security Update CD for Win 98SE and XP. It was an easy way to get up to date by simply running the CD. Service Pack 2 was also available on CD and also as a 100+ meg file that could be used by businesses for updating multiple machines. I've been intending to create a slipstream CD for XP that includes Service Pack 2 but I haven't gotten around to it.
I think that the number of patches etc that exist have serious implications for the lifetime of any version of an OS. For instance, after IBM stopped real development on OS/2 (with the release of version 4, in 1996), it became a real problem for anyone installing it fresh. I used to sell systems with OS/2 preinstalled, and by 1999, it had become a major job to do so - first modify the boot floppie (

remember boot floppies?), then do the basic install. Then install the latest fixpack (OS/2 is much better than Windows in this regard - the fix packs were cumulative, so you only had to install the latest, not all of them in order), then apply a variety of other patches and driver updates. Not only did it require pretty thorough knowledge of both the hardware and software, towards the end, it had started to cut into my (not terribly good) profit margin. The same applies any any situation where you are selling hardware and bundling software, be it OS/2, Windows or Linux. The release cycle of the OS can seriously impact its ability to penetrate the 'market' (if that's the right word in the Linux context).
Slipstream CDs are a nice option (there is now a similar option for OS/2, which saves me a great deal of time if I do an OS/2 install). However, for Windows, they're often not practical. Given the standard MS treatment of customers (and I just love dealing with a firm that starts out with the view that I must be intending to steal from them), there are many places were a standard slipstreamed disk will not work. Thinkpads (or indeed, any IBM machine) are a good case in point - they use a modified OEM copy of XP Pro. So if an install is made using a standard (slipstream or otherwise) XP CD, they will come up as non valid licenses, even using the license supplied with the machine. When you combine that with the number of machines that are delivered with 'recovery' CDs (or no CDs at all), using slipstream versions is often not possible.
This just points out that broadband is pretty much a necessity today. I can't imagine having to do updates for Windows--or downloading Linux software such as OOo--on dialup. Unfortunately, there are still many people with no options for having broadband.

I recently had a customer in just that situation. They have a machine with XP installed, but do not have broadband, and use the net only for a bit of email and the occasional bit of surfing. As a result, they had no security updates of any sort, and even their anti-virus software was years out of date. Updating that sort of thing without broadband is either completely impractical or simply enormously expensive.
Personally, even though I've only had broadband for two or three years, I have no idea how I could exist without it...
What I would like to see is more chance of upgrading a distribution on a continuing basis.
That would be great but is fraught with difficulty and danger. It's sort of like a Holy Grail.
Zenwalk hasn't been too bad in that respect. The only change that really caused problems was the upgrade from Xorg 6.9 to 7.x - too many things had to be changed to make that practical to upgrade. Even the change when Slackware upgraded its toolchain was ok, though not a job for a novice. I have two desktop machines, one of which is still OS/2, the other has been Zenwalk for the last couple of years. It is a 4.4 install upgraded to 4.8 (not going any further at the moment - JP is doing very strange thins with snapshot at present and I'm not risking a production machine until he fixes it, or I switch the machine to Vector...
paul.