Both Samsung ST80 and Samsung ST65 have 1/2.3-inch sized 14.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the ST80 and ST65 sensor size comparison.
Samsung ST80 and Samsung ST65 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.