Why does the Canon G7 allow faster shutter speed settings only at slower apertures?

I have a Canon PowerShot G7 camera. In Manual mode it supports 1/2500s shutter speed at f/8.0, whereas at f/2.5 it supports only upto 1/1600.

But, should it not support higher shutter speed at higher aperture size and maybe relatively lower shutter speed at lower aperture size?