I don't really find it misleading, but I understand what you're saying. It would be interesting to also see the stats for what websites get significant amounts of people's time, rather than just amount of data use. Obviously, data use is going to skew towards data-intensive activities like streaming video and downloading gigantic video game files.
how would you measure that? by self reporting?
"I swear, I totally didn't spend 2 hours on youPr0n yesterday" :D
Once the data is loaded, no one can tell how long of your personal time you spend looking at whatever website. It has to be measured by volume of data being transfered