I also did a check with all three sites to see what happened when I reduced the width of the browser window (Firefox 31.0 again)

The other two behaved well - they seem to have a minimum width set for the content, and when the browser window width drops below this the browser gives you a horizontal scroll bar.

So it looks like Renderosity forgot to do this. (Maybe I should have posted this one to the 'bugs' thread? Edit: posted near the bottom of page 7 of the bugs thread)

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The 3Dcheapskate (also available in DAZ and HiveWire3D flavours) occasionally posts sensible stuff. Usually by accident.
And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU.