I'm glad you were able to track down a motor and get the work done -- the total bill isn't unreasonable either.
I make a habit of checking the oil once every 2 - 4 weeks, just to minimize the likelihood of surprises. That said, I think you had a bum motor, and you were getting close to the end of your warranty so this may have happened anyway even if you were checking more -- it's hard to say.
In the end, sounds like it all worked out -- so congrats and good luck with the new motor
