It also highlights how stupid some people are if they think that installing an OS of a totally different version over the top of an old installation is a good idea. Only a complete newbie idiot with minimal knowledge of computers would actually think this is a good idea. That goes for all OSs - not just Windows.
I would concur with that from most Windows user's point of view, but it doesn't always hold.
I have had enough successes upgrading Debian based servers from woody to sarge to etch to lenny to consider it a fairly safe operation (by "fairly safe" I mean I'm happy to do it remotely, but only on machines that are not currently doing anything important - live services are moved elsewhere for a while until the new environment is considered ready and stable). I've only done a desktop upgrade twice, and while both occasions went well that is not many data points so I can't call it statistically relevant.
BUT, in every case the vast majority of the software on those machines came from the official repositories, with only a few odds and ends coming from the semi-official "backports" repos and a sprinkling of small things hand compile into
Having said all that, I still generally recommend an OS reinstall for a major upgrade even for home systems (for server use the new install option is a no-brainer anyway, as you will be wanting the new environment fully built and tested alongside the old one before migrating over) running Debian. If all your irreplaceable data is away from the system drives/partitions and properly backed up and you have all your install sets and product keys to hand you are not going to lose anything except a little time, and you get a much cleaner system (less all the collected cruft you forgot was even there on the old setup) out of it.