As someone who browses these forums on my iPhone often, I much prefer using the Lo-Fi interface.
"Power" isn't the only thing to think about when browsing on a mobile device, connection speed is also, so it makes sense to serve a Lo-Fi version to mobile users by default, if someone has the power and speed for a full view they can then switch it, but if they don't have the power/speed for that showing it by default isn't very helpful as it will take a long time to load/render before they can switch.