I can rotate objects totally smoothly without any wobble. What browser are you using? The hotspot position should not affect wobble.
Hotspots are set to the nearest pixel. If you can put them a fraction of a way through a pixel, it means the object is shown at a fraction-of-a-pixel offset. This can cause blurry graphics on some browsers (annoying for pixel games) or other issues like the platform movement "floating" by a fraction of a pixel above the object, because the platform movement only works by whole pixels.
The way the math works out, when zoomed in, a pixel's position is its top left point. Consider the very top-left most pixel: you probably want the hotspot at the top left of the object's bounding box, not appearing a small way inside the object when zoomed in a long way.
Does that help? There should be no wobble no matter where you put the hotspot, that's a different issue (or so I thought). All objects are drawn from their top-left point, so it doesn't matter where the hotspot is, it just changes the math for calculating the top-left point, and that is calculated with floating point precision.