They take a 95TH unit, and re-tune it and it's a 110 TH unit. But they sell it for thousands more.
...
Almost got it right but no cigar.
There is more to it than that, the faster miners are using better grade chips that can run faster and still be stable. Same thing is done by CPU makers, the various speed CPU's in any 1 family are not different versions- they are the exact same chip design that during testing are binned (graded) for speed and stability. Some can run faster than most, most are on-target and some are slower. No matter what they are all chips have design targets that state min, avg, and max performance to be considered a usable chip and the chips are graded and priced accordingly. Fact of life is that in any given production lot there are far fewer grade-A chips (best) coming off the line than there are grade-B (avg) or grade-C (usable but...)
Sure software tweaks can make a miner run faster than what the mfrs sold it as, question is, how stable is it? Same applies to OC'ing your CPU or GPU's.
That's mostly a myth. While it's true that they can, and do use chips that aren't able to achieve peak performance, in most cases that's just not the case. Most fabs have very high yield rates these days, and they just don't have enough lower spec chips to meet demand, so they typically use the exact same high performance chips and de-tune them for a lower speed.
Why? Because they can sell more of the lower speed units than they can the higher speed units, and by controlling the firmware they make sure people aren't buying the low speed units and clocking them up.
Simply put, not everyone can afford top of the line, and there are more people looking to buy less expensive than more. Even if you can afford it, many people prefer the lower speed to save on power and/or heat dissipation.