There's an old thread here in the lens section that goes something like this:
Poster 1: I have this lens and I can zoom from end to end without refocusing.
Poster 2: You are wrong. I have this lens and I have to refocus.
Poster 1: I'm right. And when I bought it, the dealer said that was a feature.
Poster 2: Have you had your vision checked recently? This web site doesn't say anything about that feature, therefore the lens doesn't have it.
Poster 3: Here is the wikipedia entry on parfocal and varifocal. Honestly, is it a big deal to refocus?
Poster 2: Yes, and I have returned this lens, sold my Pentax and bought some hyperexpensive thing for just this feature. My standards are exceptionally high.
Poster 1: I've had 11 National Geographic cover shots with my copy, and I have never changed focus since the day I bought it.
After that, the thread starts to deteriorate.