I don't believe that question is a good example of a question that isn't about Ubuntu. Ubuntu is currently installed, the longhand way of reading the question could be: What do I need to do to Ubuntu to get rid of Ubuntu and prepare for the reinstallation of Windows?
And that might very logically have plenty of Ubuntu-related things in its answer. You might need to unmount the firewire matrix from /proc/, or defragment the boot partition, or patch the 802.11 antenna array for parity switching. The person asking doesn't know. That's why they're asking. In short, that the answer doesn't neccessarily need to be Ubuntu related, doesn't mean the question isn't on-topic, even if only tangentially.
I also have to think about this from the perspective of what makes the internet —and AU— better. Neither deleting a furiously popular question with good answers or even just shoving it to another site (where its search exposure will suffer) accomplishes this. They're bad options that tick an administrative box.
And even getting rid of answers that aren't Ubuntu —just because they aren't Ubuntu— seems a little rigid and unhelpful to users who use the site. You've targeted an answer which does its very best to be helpful for the problem at hand. That's not something we should punish or push away.
The second example is a better candidate for going elsewhere. It's as much about BIOS as anything else.
The third example is data recovery and with the current OS being Ubuntu so is on-topic here, IMO. At the very least options can be presented.
And the last one seems to be more about creating a bootable Windows USB. I'm not sure if that's from another Windows install or Ubuntu, so again, potentially on-topic.
To summarise, keep an open mind and wear sunscreen.