Service Pack 3 was released over two years ago! (A year after Windows Vista shipped and FOUR years after Service Pack 2 shipped.) Anyone who is serious about their computing environment has long since upgraded to XP Service Pack 3 (or to Vista, or to Windows 7).
Just because you changed the oil in your car the last time it was recommended doesn't mean that you shouldn't change it this time. Nor do you expect to get the oil for free!
Microsoft has offered free updates to Windows XP for 9 years now and has promised to continue to do so for four more years. Microsoft is not forcing anyone to do anything but when you disregard the manufacturer's recommendations, you take unnecessary risks with your investment.
If you are a consumer, the risks are yours and yours alone. When you are a business, failure to observe Microsoft's recommendations place all of your business data and the personal data of all of your customers at risk. The potential impact of a loss of this data can be profound.
I just don't see that anyone still running Windows XP (for whatever reason) has any right to gripe because Microsoft asks them to upgrade to SP3 in order to continue to receive support. (Nobody gripes at Apple for having the same attitude about far newer code than Windows XP SP2.)
Sooner or later, Microsoft has to pull support for old code and six years after XP2 first hits the streets strikes me as more than reasonable.
We are in the software business, and although the situation is a bit different, we build development systems that run on Windows, Linux, Unix and VMS, so we support a lot of OS platforms. We have yearly releases of our products to resolve problems, add features and to support new ports of the different OS platforms. Being pragmatic, supporting a lot of old OS platforms is problematic from a support point of view -- it is not feasible in the long run.
The upgrading to XP SP 3 is relatively painless, at least in all the XP SP2 to SP3 upgrades we have done, as it is not destructive and does not require a clean install like going to Win 7. Sooner or later the SP2 guys are going to need to suck it up and move-on, and going to XP SP3 is about as benign as you can get. That is my opinion.
We've had multiple occurrences on the retail side of our business where customers bring in old PCs. When we put SP3 on them USB ports stop working correctly. It's not an uncommon issue (do a quick Google search and be shocked at the number of results).
I'm not sure that this attributes the large percentage of SP2 computers in your article, but it doesn't keep the number down by any means. We've been pushing Windows 7 (and Vista before it) but sometimes its either support the customer or lose the customer. And I'm the one these issues get escalated to.