Had to replace the alternator and battery in my 2007 Mazda 3s Sport, with only 43,000 miles. What a bummer! Has anyone else had this happen? I'm aware that parts do not last forever, but this seems a bit far fetched.

 

Definitley a bummer, but not completely out of the ordinary. The factory batteries are typically low quality. They can easily go bad after 3 years. Once a battery is bad the alternator gets to work overtime and that can kill it early.
You may have had some indicators of a bad battery and you did not notice. I. e. the lights go bright and dim with the speed of the engine.
Make it a habit to have the battery load tested every fall.

 

I have 60k on my '08 and no problems in that area.

 

ive went though 3 batteries in my 06, stock alt still, no draws. I just hope someone didnt sell you parts you didnt need