Crow Hunter, and others:
While I don't doubt you all own variables that have held up well, because I own a number as well, all I can do is report what I've seen, and not just with my scopes but those belonging to other people.
Thanks to my job, I've been in a lot of hunting camps all over North America and bunch in Africa as well, often with people who felt they had to step up in rifle-power because they were hunting animals larger than deer. Have seen a number of variables fail on expensive hunts, and none were so-called "affordable" models.
In fact, scope failures have happened on over half the African hunts I've been on, twice to me. On my hunts one scope retailed for around $600; on the other the scope cost around $1000. Not-so-luckily, on both hunts I'd also brought along a back-up scope, in each instance a small fixed-power, so it wouldn't take up much room in the gun case, so could continue hunting with my own rifle.
But none of the other hunters brought a back-up scope, because they had complete faith in modern variables, so had to borrow rifles to continue hunting--in one instance one of the two rifles I'd brought. The failed scopes were mostly mounted on hard-kickers, including a couple of .375 H&H's and a .458 Lott, but one was on a .270 Weatherby Magnum, and another a 7x57. The scopes were of various brands, but the one thing they all had in common was owners who said, "Gee, I've never had a scope fail before."
In contrast, the only fixed-power that "failed" on any of those safaris had troubles because the hunter fell, bending the front end of the scope slightly. It went out of zero, but a few shots had it sighted-in again, and it kept on working for the duration of the safari.
Another thing I've noticed is a substantially higher failure rate in the last decade or so. During one 2-year stretch during this period, when my wife was also writing about optics for a women's hunting magazine, we had 6 new scopes go bad.
Another example came from one of the many readers who contact me. This was a guy on the Campfire who'd bought a new .30-06 of a make known for accuracy, but couldn't get it to shoot, despite the bedding and everything else checking out. He asked about a good load for 165-grain bullets, and I gave him the standard 57 grains of either IMR or H4350. He reported back that wouldn't shoot either, so I asked if he'd tried a different scope. He said he'd tried two, and the rifle still wouldn't shoot. I said it was too much for me without actually being there.
Two months later he PM'd again, saying he'd tried a third scope, and the rifle suddenly started shooting sub-inch groups. At that point he confessed the first two scopes had been brand-new, never previously mounted on any rifle.
I suspect this increasing failure rate is partly because of higher demand for shooting equipment in general, resulting in companies cranking out more scopes, and new optics companies appearing all the time. But in the past 10 years, scopes from companies I used to consider pretty much infallible have failed, and more than once or twice. Again, the vast majority have been variables, including FOUR from a company that doesn't sell any scopes retailing under $500.
Some additional evidence for this "crank 'em out" hypothesis is the number of brand-new scopes that failed within the first two boxes when mounted on harder-kicking rifles. This usually indicates the scope wasn't assembled properly in the first place, and in fact in a couple of instances where the scope company reported on what went wrong, it turned out to be a loose screw somewhere.
Yes, many variables--even inexpensive models--will last a long time, especially on a typical "deer rifle" chambered for a cartridge smaller than any .300 magnum. But that doesn't mean they're infallible, or as tough as any modern scope.
