There is many that say 2 subs is the best way to go. Can someone explain this philosophy a bit more (simple terms preferred)?Yes. If the subs are asked to go above about 80Hz they will begin to attract attention to themselves. At this point you'll need two, one for the left and right in the same vicinity as your main speakers.
If the subs have no output above 50-60 Hz it won't matter where you put them so long as you can get the bass right at the listening chair. This might be hard with only 2 subs; very easy with 4 as discussed prior in this thread.