Five gets you
10 there is a hidden screw under a foot or behind a label.
 
 This is also the same for the Atari 5200 power supply.  Two screws are
 plainly visible but the other two are under rubber feet.  Arrgh! 
 
It's very common. I seem to remember, for example, that the HP110 laptop
has 4 or so clearly visible screws on the bottom, and rather more hidden
under the feed, the nameplate label, and a couple of other stickers.
Certainly I always peel off feet and labels if something won't come apart
after remocing all the visible screws.
-tony