This is what an old style REAR Hub looks like without the gears. The Gears thread onto it on the right side. Notice the offsets: On the Right, it is to accommodate the gears. On the Left, it is to help make up for the offset on the right. The Bearings are under the threaded portion of the hub. Notice the distance from where it attaches to the frame and where the bearings are. It's over an inch. This style system has been around since 10 speeds first came out. We had problems with it then, but now we have 8 gears instead of 5 back there, so the extension is longer.
On new bicycles we have 21 and 24 speeds instead of 10. The pedal arms are longer, the gear ratios are lower, the tires are wider and theoretically, the bicycles are more capable. But the old style system, that wasn't very good back then, is really out of date now!
If you have a newer bicycle and you ride it off road, odds are you will damage it just by pedaling it. This is because of all the leverage you can put on a drive train that was originally designed to be used with 5 gears, not 7 or 8 and was designed to be ridden on the road, with skinny tires, not in the grass or dirt with a high traction fat tire.
The above picture is of that part, which I spotted on the warehouse floor and the hub it belonged to. This was off of a 6 month old bike, a MONGOOSE from a discount store. It apparently bent and then broke from the stress of use, and the owner of the bike said he hadn't gone off-road. He was put out and lamented, "I guess ya get what ya pay for..."
Yes. You "save" up front, but pay and pay in the end.