Hey dances with cats I am glad another locksmith is here on the board.
If your ever up to moving to North Alabama we are hiring 
Anyway off to the OP:
Your screen door lock is most likely a wafer style lockset being mounted upside down is no big deal since wafer lock springs function a bit different.
Knob locks and deadbolts are another matter. With the sping and pin on the bottom (key teeth facing down) over time debris does get into the lock, this is not a major problem that will make the lock fail overnight. Also, the spring s will start to compress not pushing the pins up all the way up. When this happens the lock starts to fail.
From person observation an upside down lock will fail on average 3 years earlier than a normal residential lockset. (they usually last on average 10 years)
Why are they mounted up sidedown? While many locks are universal in their handing (left or right handed door) such as weiser and schlage Some locks such as quickset and titan locksets are pre mounted. They do require a special tool to remove the cyl housing and putting them in right side up.
Commercial key and know sets are also handed. They can be corrected with a key and an icepick and knowing how to do it, some contractors really do not care or do not know how to change this.
Having the lock upside down in my opinion is bad… but not such a horrible thing that you should be losing sleep over it.