What do you mean it does not have have an aperture? Don't all the cameras have it?
No.
None of the IXUS have an aperture, nor the A450,A460,A530,A550 or A560
do you mean we can't set it manually? (see http://www.wrotniak.net/photo/snap/a460-rev.html, it mentions aperture as well)
That link actually says "For example, at the widest angle it will use either F/2.8 or F/8, and nothing in-between.
This indicates that the camera does not have an iris diaphragm, but just a swinging plate with a single opening"
He is not quite correct.
There is no swinging plate with a hole, just a 8x ND filter that swings in or out.
For optical reasons, the effective aperture of the lens changes as you zoom from wide-angle to telephoto, but that has nothing to do with an iris diaphragm.