......I love my Glocks and they work great, but, for reference, there's actually more frame mounted steel rail bearing surface in the smallest poly Kahr than in any current production Glock.
From the trigger forward, there are complete steel rails on each side that ride in the cut outs on either side of the front of the slide. There are also rear steel rails/inserts on either side at the back of the frame. The polymer "rails" in between serve no structural purpose other than making the slide easier to guide back on during reassembly. In fact, when I asked Kahr about this, they said those poly "rails" could be completely cut out and would not affect function in any way.
That first paragraph of your quote could be telling us something about differences in known reliability and service life between the two brands. I will grant the fact that the smaller Kahrs probably are stressed harder than their larger Glock cousins--just because they are approaching design limits due to small size.
I'm not necessarily going to buy Kahr's (or your) assertion that the *only* reason the plastic slide rails are there is to aid in aligning the slide upon reassembly. I do think that might be a secondary benefit, but stiffening the thin, small plastic frame might very well be the primary reason for them. Even the longer (than Glock) steel rails up front could be an attempt to strengthen the frame or provide added longevity.
I do not argue with their assertion that the gun would run w/o the plastic in the rail area--but would it reduce service or frame life? Perhaps the overly generous (??) use of metal and plastic in the rails (in comparison to a Glock) could be contributory to the plastic Kahr's well known failure to go completely into battery problem.