I've seen office professional for 15 bucks, I wouldn't say $25 for the basic version is a good deal… Especially considering you end up with a Microsoft product.
And the best part is that while the key is valid, the license isn't, so technically you're paying for a pirated app
(Explanation: those keys come from msdn or from a Microsoft partner action pack - they activate and look legit, but are licensed only for development and internal testing for that company)
The idea is that even if you're using pirates windows, you're still in the windows ecosystem, you'll be more likely to pay Microsoft for other things. So in a weird way, yeah you didn't pay for windows, but you also didn't buy an Apple either, and now you're using windows apps and programs.