They are tuning for safety as they perceive it . Give one mechanical reason why the SPECIFICATIONS listed by the manufacture would lead to early demise. A RANGE of valve lash settings exists. Just as oil. Inside the high and low marks, accepted.
I at least postulated a theory as to Why the tight end is better for longevity. You quoted an unconfirmed consensus.

One possible cause of the "dropped valve" might be the worn exhaust rocker providing way too much valve clearance - this would prevent the cam from gently lowering the valve down onto the seat, and the valve would close more aggressively than it would with proper clearance.  If we can find that other dropped valves also had a worn exhaust rocker....that might be an indication of the cause.  The bike that I just purchased and brought out of long term storage had a badly worn exhaust rocker - but I checked the valve clearances before I took things apart and the clearances were not excessive....that might be an indication that someone adjusted the valves and corrected for the wear in the rocker.

When I adjust my valves I try and get them closer to the minimum clearance so that the engine makes less valve noise.  The clearance is supposed to be between 0.003" and 0.005", I have a 0.003", 0.004" and 0.005" feeler gauges.  The 0.003" is very flimsy and hard to work with - so I use the 0.004" and try to get a pretty tight fit....and once I get what I believe is close I try the 0.005" and I don't want it to slide through at all.  I want the 0.004" to slide through with some tightness, and last I check the 0.003" and I want to to slide through with just a bit of drag.  

justin_o_guy2 wrote on 10/29/15 at 22:46:32:

because looser lash gives more room for error
adjust loose and get it off a thousandth and you have a slightly tighter or looser clearance than you expected
Adjust for minimum clearance and get it wrong on the tight side and you get a non running motor and maybe a hole in your piston or burned valve

what do you prefer, loss of maybe a 1/4 HP, or loss of an engine?
I tend to go with the several thousand guys who say 'go loose'

though in truth I prefer the middle of the road valve lash, like Dave, that way I'm neither loose nor tight

no, you got the following:
adjust to the tightest possible clearance, and get it wrong, you can wreck your engine
That's a valid mechanical reason not to go to the tightest clearance
you might never get it wrong, but others are not old hands at this, and can
I have watched newbs force feelers between valves and adjusters thinking they weren't using excessive force, and then wind up scratching their heads;
I never said you were wrong to adjust tight, I said I and MANY other folks with mechanical experience prefer a bit more leeway, and FOR SURE I wouldn't advise a newb to try for the tightest possible clearance
Then there's also the question, does the engine loose or gain tolerance as it heats up?
I don't know the answer to that, and I'm not opening a hot engine to find out, I simply stick with a middle of the road adjustment, so I know absolutely I'm neither loose nor tight

Remember the guy on here recently who let a 'mechanic' adjust his valves and the cylinder pressure went form 180 to 72?
THAT'S why I don't try for minimum tolerance

yep, that's the difference between someone who loves fiddling and someone who doesn't
There's nothing wrong with running minimal 'in spec' clearance, and for the record, I believe you may be right about extending the valve train life that way, so long as you're anal about checking yourself, and you don't sort of 'overrun' service intervals at times
Me and you also have differing experiences with valve train clearances
The bikes I've had that I actually had to do a few adjustments on were 'shim over bucket' designs, and the clearances always shrank over time
the 'screw type' adjusters I've worked with were in old car engines (iron block, iron head) and those also shrank over time, aside from one old Chevvy that one of the adjusters started mushrooming pretty quickly at the tip (THAT got replaced)
you on the other hand have seen clearances grow, IIRC other discussions we've had about it
so in my case, I always went to the loose end, and waited till the clearance shrank to the tight end, then readjusted
Now that I'm  a little less sure of myself and a bit more cautious, I tend to look for the middle ground when adjusting valves

I put them in the middle,... one way will give more lift, and make more power,.. but the vales need seat time to cool...
..'course, I check them so rarely... who knows where they wander off to... ...

Dave, how tight is the valve guide?  I had a Subaru that would get an intermittent misfire on #2 cylinder and it took the dealer for ever to find it.  Finally found the guide was loose and would intermittently slide out with the valve and sometimes hold the valve open causing a misfire that the ECU would record.  Is it possible the guide slid out and held the valve open and the piston went smack and snapped it off?

This isn't my bike....I grabbed the photos from cadence, he is parting this bike out in the Marketplace.  He bought the bike this way and will be building an electric bike with the parts he keeps.
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1444532386

He states the lady he bought the bike from was riding it, and then it just stopped.