Yep, there's a bunch of reasons... Here's mine:
The Warns are a known name brand, and have served many people well for many years. That being said, the stresses put on hubs by our trucks can be severe... severe enough that the Warns will break with enough abuse. However, not everyone sled pulls, runs 37" + tires, has over 1000 ft-lbs, or offroads heavily... and for them, the Warn hubs will work great!
However, if you have increased power/torque output substantially, are running big tires, or sledpull and offroad extensively, you're money ahead to step up to the Dynalocs.
The Warns stick out about 3/4" farther than the Dynalocs, and are surrounded with a chrome plated plastic/cast metal casing. An unplanned meeting with a rock or other obstacle will not go well!
The Dynalocs are a solid machined piece that will take significant abuse and keep asking for more!
Here are some pics sent to me that show the two. All pictures are with hubs installed on a Power Wagon with stock wheels/tires.
Warn hubs:
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Dynaloc hubs:
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I love the way the Dynalocs look almost factory in the above picture. They have a much more positive engagement mechanism than the Warns, and have Chromoly innerds. Dan can explain the particulars here much better, but they're strong.
The Dynaloc hubs fail in the "locked" position, in the unlikely event one was to break. Thus, you would still be able to get out of your situation and back home without a long walk.
In short, if you have a pretty much stock truck with just a few performance mods and generally stick to the street, the Warns will likely give you many trouble free miles of great performance.
On the other hand, if you're running greatly increased power, big tires, and really use the truck to its full capabilities, the Dynalocs are the way to go.
Plus, the machined Dynalocs just look cool!
Hope this helps...
--Eric