When sitting in that job interview with a prospective employer, you can't even be coy about what you used to make, since the new employer can just look it up on Buffer's site... "oh, you made $128k at Buffer. We'll pay you $129k"
Except your actual sample number is wrong -- you must not have read the original post. They're hardly even paying anyone the market rates for SF. Their highest paid engineer, a "senior" one at that, is only getting $107,9k, in SF!
So, it's more like, "oh, you made a $96k at Buffer? We'll pay you $97k"
Although on the other hand, for a gaining company, it's also a matter of providing competitive compensation for employee retention purposes, so, even if your old salary is posted somewhere, a new company isn't necessarily going to employ you at the lowest possible cost, since the likelihood of you leaving for competitive pay would be higher, and turnover is expensive.
Lots of folks confuse bad management with destiny. -- Frank Hubbard