It would appear that the play in the slides totally depends on the mechanism used to control the slide. Perhaps the rack and pinion drive type are more susceptible to movement and so the slide locks are provided by FR.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW