I want to say that the question is about the guys who get on the sides of their feet. That is the only way I can think of that the knees get noticeably out in front of the toes. In a good, solid, athletic receiving stance, your knees should be slightly in front of your toes. If your knees are not in front of your toes you will not be able to balance.
I think you're talking about when guys use their whole foot on the ground (ball to heel) and roll the ankles so the inside of the ankle is closer to the ground. This looks cool, but I think that it is much tougher on the knees than staying on the balls of your feet with your butt low. It's really tough on the ankles, as well. I think that catching in this manor will make it harder to block, as well as make it harder to use any ankle sway while receiving pitches that are not in the dirt.
How I tell my catchers to get in their receiving stance:
1. Stand straight up
2. Feet slightly wider than shoulder width apart (find how far is comfortable for you)
3. Keep your right foot slightly further back than your left. (Cut your left foot in half with your toes. How much you cut it is based on your comfort, so long as your right toes aren't completely behind your left foot)
4. Bend at the knees with your butt as low to the ground as possible.
5. Get balanced on the balls of your feet. (You won't be able to balance without being on the balls of your feet.
From there you lean forward to where you need to be to balance well and not be up too tall, and you're ready to go.