"What's with the lock on (new) S&W's?"
Why, generally a little plastic bag with two keys.
Also... the company that own's S&W is named 'American Safe-T-Lock'.
I have more with the 'Infernal Lock' than without - and none have caused me any form of grief. I wouldn't specify a lock, given the choice. But... I won't let it's inclusion deter me from a new S&W purchase - they make some fine new revolvers these days. I also don't let Ruger's poor QC deter my new purchases... I just keep the tool box handy. Sadly, every Ruger has needed sometimes a lot of TLC - those 'lock equipped' S&W's worked fine right out of the box.
Stainz
PS The little 'L' is on the 'left' side - above the cylinder release... handy reminder of which way to grab the revolver - for the easily confused, of course.