I'm not familiar with the iPad charger, but the Surface chargers do not have holes for cooling, so they need to have a certain amount of surface area for sufficient cooling. In other words, a similarly constructed charger with the same wattage but less surface area would run hotter and that could lead to reliability issues.
Very true. I forgot about that.
While I agree that the SP2 needs the power, why does the RT/Surface 2 charger still need to be as big. It's a ARM device like the iPad, so in theory could have a much smaller charger right?
The Surface 2 has fast charge, which means it require more power. The iPad was designed to be charged over 5V lane of the USB plug. The Surface 2 can't do this due to the fast charge.
In addition, Apple cheats. Like their MacBook Pro's. If you push the system to it's max, the charging speed is drastically reduced, to even a full stop. There was a generation of MacBook Pros several years ago where you could change the battery, where the system would throttle down if the battery was not in, while plugged in, as the power adapter could only deliver 85W and not 90W. Meaning it was drawing more power from the battery. So if you are pushing the system under heavy load for a lot time, you are were depleting the battery, and not charging it as you would expect as you are plugged in. But as those who actually use the Mac for intensive tasks uses the MacPro, or don't push the laptop to it's max continuously, and with a fan base that hides issues under the rug, it was not an issue that concern many or anyone.
The iPad power adapter is 12W, to support older iPads which were operating under 12W max (now 10W). The Surface 1 and 2, operated at 24W under heavy load and fast charging.