I'm going to go out on a limb here to back the previous poster before you and say that its not too far fetched to completely discount what was said. Web sites poll the browser on the device you are using to determine what browser its using, what resolution and what mode its running in, and then will reformat or redesign their content to better fit and work for the specific browser. The Web sites may not only reformat, but they may also reduce the color depth (4,096 versus 65,536, versus millions of colors, for instance), or drop background colors altogether and opt for white backgrounds, remove video or picture content, back off on advertising or change the advertisement to target the mobile user for instance rather than the stationary one, use your GPS to find content advertising that is more specific to your location, etc. So if you're running a "mobile" version of the browser on you're phone, and the tablet is running the full blown version of the browser such as Firefox, there could conceivably be considerably different amounts of data being sent to the two different devices.
Just saying...
Sent from my DROID RAZR MAXX using Xparent ICS Tapatalk 2 with Google voice to text translation. Please excuse any minor spelling, punctuation, capitalization or grammatical errors.