It may be pretty hard to compare US and foreign offers. For instance, in France, you'd be earning 36000 euros in cash --what's landing on your account --, however it would actually be nearly 48000 euros with charges (that's what you're taxed for): social security, retirement, etc. Then the company will actually pay some 20000 more euros in other salary charges. That means that 36000 euros in cash in France translate to (36000 (cash) + 32000 (charges)) * 1.30 = about US$ 90000 ...
That's the same everywhere (well the extent varies, but not by the margin you suggest), which is why you should quote your gross pay (i.e. the amount before deduction of social security, pension and related costs). On top of that there's extra costs for the company obviously, but those are not 'wages'. Quoting the gross salary is standard here in the Netherlands because the amount that is left after taxes varies depending on personal circumstances. In the Netherlands (and Belgium and to the best of my knowledge France) the contributions are withheld by the company, in the US you pay them yourself. Quoting the gross salary makes for the best comparison (not perfect, but better than stating net pay, i.e. the amount you are paid each month - that number is in this context meaningless).
Wow, double of the gross salary?
So a company paying me $80k (out of which I have to pay taxes and I net let's say $60k), actually pays $160k? Seems like a LOT to me.
In Italy it's around 1,46x the gross salary.
A productive employee costing double salary, fully loaded, includes a benefit and other direct load (employer FICA, UI, 401k and health insurance, ...), plus share of supervisors, plus facilities. i.e. a team of 5 developers requires maybe one full time equivalent manager making roughly the same or slightly more, who also has his own benefits, office space, etc. And his own manager, etc. (assuming a reasonable span of control, like 5-10:1 manager)
I usually use 1.3x for "direct loaded cost" and maybe 1.5x for facilities and loaded cost. In a "below market compensation" environment, like a startup, the loaded costs are usually higher (if you pay yourself $30k at a startup, you still probably want the same quality health insurance as if you pay yourself $60 or $100k, unless you're young and single and get an HSA/catastrophic coverage).
Including supervisors and other operational staff into an employee's fully loaded cost makes sense for project billing purposes where the cost of supporting that engineer's work must be taken into consideration. For the purpose of this discussion, that must get excluded since offer letters don't state salary that way.