What I just realized is that they (I refer to those guys behind the curtain off course) provide several alternatives to deliver the message. Like:
- Help us provide free content to the world by donating today!
- You can support Wikipedia by making a tax-deductible donation.
- Help us improve Wikipedia by supporting it financially.
- Your continued donations keep Wikipedia running!
The position of the message is also nice. On the top left with readable small font. The italic style makes it stand out without irritating the eager eye looking for valuable information.
Click the 'donate' links on those messages and you will see a video of Jimmy Wales, the founder of Wikipedia explaining the purpose of the free encyclopedia and the needs for donation. (Hey, Indonesia is in the video :D)
Imagine a world
in which every single person on the planet is given free access to the sum of all human knowledge.
— J. Wales, Founder of Wikipedia
I hope I help them delivering the message by making this post :D