Quality of the parts and weight.

You start off with basic hubs that use traditional cone/race bearings with less expensive steel axles, steel spokes, and good rims that aren't as light as they could be. Keeping in mind, heavier rims and tires are less efficient than lighter ones. Lighter means you can accelerate faster and climb hills with less effort than you could with the heavier rims. Hub weight isn't as big a factor.

As you move up the price index you start to get into hubs with sealed bearings, stainless steel or aluminum axles, stainless steel spokes, and lighter weight rims with machined sidewalls, etc...

If you don't plan to do a lot of riding, will limit riding to fair weather and aren't interested in "performance" the basic wheels are OK. However, if you plan to log higher mileage, ride in wet conditions or are looking for more efficient wheels the mid to higher range wheels are the best bet. Good wheels are a good investment, second only to a good frame and fork.