Tony;
We call them "swevil" wheels. Emphasis on "evil". They are a bear to manufacture, run the cost up, and protrude way out in front of the deck. In addition, they allow the machine "free reign" to seek the path of least resistance, making the machine "hunt" and requiring constant diligence from the operator, especially on the side of a hill. Other than that, they are great.
The trick is to place just enough weight on the front wheels. This is accomplished by using the engine as a counterweight, the rear wheels are the fulcrum. We have the weight distribution just so, and turning is no problem at all.
These concerns are common in the marketplace; but the swivel wheels that you see on the competition are a response to a perceived need and consumer demand, not actual need. The exception are the direct drive mowers with the motor on top of the blade and much weight on the front wheels. However, that market is price driven, and very few direct drive mowers have swivel wheels, though they would benefit most from them.