Return trip

I received an email from Delta airlines this morning, informing me that I could check in on line for my return flight to Gulfport, Mississippi on May 31, 2013. Obviously, when I booked my retirement flight home for January18, 2013, I had to book a return ticket as a return ticket was over half the cost of a one-way ticket. I still cannot figure out the logic or how a return ticket is half the cost of a one way ticket? But then again, there are so many things that defy logic. Also wondered why airlines allowed passengers to board a flight from the front even though it creates congestion in the aisle for those boarding later. I am told that the reason for this practice is that if you allow people seated in the back to board first, they will put their carry on luggage in the first overhead bins resulting in no space being available for the front seated passengers.
Anyway, I will not be checking in for my return flight so someone who might be on standby can have my seat.