I don't know who the person talked to at Smith & Wesson but he or she should read their manual before making a statement like that.
Here is what S&W says about +P ammo in their 38 special according to there online manual.
“Plus-P” (+P) ammunition generates pressures in excess of the pressures
associated with standard ammunition. Such pressures may affect
the wear characteristics or exceed the margin of safety built into some
revolvers and could therefore be DANGEROUS. This ammunition
should not be used in Smith & Wesson medium (K frame) revolvers
manufactured prior to 1958. Such pre-1958 medium (K-frame) revolvers
can be identified by the absence of a model number stamped inside the
yoke cut of the frame (i.e., the area of the frame exposed when the
cylinder is in the open position).
So, any revolver model 10 made after 1958 is safe to shoot +P ammo.
Now I am going to let you know the real story. S&W has been heat treating cylinders at least since 1930. Also, todays plus P ammo is what standard pressure was back before 1972. I am going to give you a link from a well known member on this forum. He has done a lot of research and is knowlegeable on this subject.
Shooting with Hobie