I just came in wondering the same thing but not only about my iPhone 5, but my mid 2010 MacBook Pro. It's completely updated, I have a wireless N router and a 100 Mbps connection that seems only my budget level Acer laptop can reach. My Acer is only slightly newer but still pales in comparison to my MBP.
My iPad, iPhone 5, and my 13" MBP (the last Core 2 Duo model with the Nvidia 320M). My cheap Acer that I'd rather carry around to surf and goof off on is the only one that can break the limits of my Apple products across the board unless directly connected to a open Cat5 connector on the provided Docsys 3.0 wireless gateway provided by Comcast/xfinity.
My cheap Acer Windows notebook shows the proper speeds I should be getting but between my iOS devices and my MBP, it just doesn't make any sense at all.
My iPhone 5 reaches around 60 Mbps and had been thinking if throughput was upgraded on the 5S. My iPad 2 has somewhat similar performance.
Much to my annoyance as distance from the wireless gateway is around eight feet away or less depending where I hit the Lazy Boy (I had gotten this new gateway since my old D-link was causing a bottleneck)
A promotional email from Comcast had told me that they had doubled my speed from 50 to over 100 Megabits and I was shocked at my Mac let alone my iPhone 5 had shown no improvement but the update was there as it worked very well with my Acer laptop that all were tested using Firefox on Mac OS X and Windows 7 Home Premium. My iPhone 5 should reach those speeds I would assume along with my iPad 2 (older 64GB model) and even a Galaxy Tab 3 running Android Jelly Bean.
Comcast has tested my modem and sent some oddities to it for it to restart completely. Still, I just don't get it. on the flip side, my upload speeds are awful, barely reaching over ten Mbps on any device.