I'm not surprised. The English lyrics are, frankly, a little awkward. Nena's accent could be seen as endearing, but at the same time, it sounds a tad stilted, and nowhere near as fluid as the original German. It's a dance tune, and once you know what the song is about, it's just much more fun to hear it in the language that sounds more polished and lets you tune out the words so you can, well, dance.
At the end of the day, lyrics are a much smaller part of the musical experience than people give them credit for.
Then again, I have a very easy time dissociating lyrics (and their meaning) from the rest of the music, so maybe that's just me. This doesn't always happen, but it's not unusual for me to listen to a song enough times to internalize the syllables and sing along, and still not stop and think about what the words actually mean (even in English). It may sound odd at first, but when you think about it, you probably have the same experience when you go to the opera - try and make out the words of Handel's "The Messiah", an English opera, and you'll see what I mean[1]!
(And now that I think about it, how many people know what the verses of 'Born in the USA' are really about?)
Also, I did already know that the German version was more popular, so it's hard to be sure I'm not just rationalizing that knowledge after-the-fact! :-)
[1] http://www.youtube.com/watch?v=x5jeelU1Vb4