When using data (not WiFi), images on the page can be compressed by the network to reduce the amount of data you're using. As far as I know there is no way to disable this unless the network supports it. Such as, my 3 dongle for my laptop tells me when images are compressed and I can disable compression (increases bandwidth usage/charges)

On WiFi I am not aware of any compression as bandwidth would be unrestricted. The only other possibility would be that certain sites are treating you different for being on a mobile device.

 

I've honestly never noticed any AA when browsing web pages. Especially on images. I could understand it on text as a lot of things use AA on text to soften the edges and make it easier to read.
Could you provide a side-by-side comparison to something else showing the same page? Or show me a page we can compare with a screenshot of our screens?

**Update: Actually just checked it and I can see what you mean. Just went to google and viewed the logo and if you hold your finger on the screen (dont need to move around) it turns off the AA. I had never noticed this on any other sites until you pointed it out. I guess the quality of the images isn't as important to me.