The number has been floating around here and there and I've even heard that number being used by a temp agency a while ago when I inquire about actual job opportunities for "my brother" (heck, they don't have to know I'm looking around for myself), but they gave me that 75 to 80% number as well and thus "a slim chance" and my best bet was to look for support through the government, since they are not skilled to help people on the spectrum for work. And this was from one of the bigger temp agencies in my country.
Where they got their number, I don't know... and it makes one wonder if they carelessly throw around that number themselves. However, they might be talking from experience, as their database probably notes any peculiarities for individuals.
Now, the number might be that high because; it's not like they listed everyone on the spectrum worldwide. Nor is everyone, who might be on the spectrum (since diagnosing is not a mandatory process; nor does everyone "suffer" so they need help) but is employed listed.
On the other hand, even if you're speaking of 80 percent, it's still 8 in 10.. of 4 in 5... which IMO is too much. In an ideal world everyone should have a job they enjoy and that works for them. But alas, it's not an ideal world.
The other side of the coin is this though. People sometimes point out that, there are many high functioning ones have a job, and they might negate that high number, but they simply don't get involved with this researches and polls. And that's a fair point. However, there might also be a fair amount of aspies out there that are recluses and don't even interact with "the real world" that much, hence they're not even on the radar at all as well.
Furthermore; and this is where I think it gets interesting, especially with the changes in the DSM 5. For a diagnosis to hold some ground, one of the criteria should be that it has to impact your life. (DSM 5; Autism spectrum disorder 299.00 section D. Symptoms cause clinically significant impairment in social, occupational, or other important areas of current functioning.) and this if you are able to hold a job, are you even on the spectrum? Yes, we're not going to retroactively take away diagnosis, however, by definition, one can wonder if you can even speak of people who pass criteria D (as well as others) if there's much to diagnose anymore. And the way I see it, if you're socially inept, much like Aspergirl4Hire points out, you might not be that succesfull in employment, as a lot revolves around social behavior, not so much skills.
I also feel that the aspies who manage jobs and especially higher functioning ones (both jobs, and individuals)... to me it comes down these people being so skilled, that their skillset is so valueable employers might put up with some odd traits someone has. That's not that uncommon. A bigger question is, and perhaps more important now; how do people hold up if they're all held against the same light? Some might require support but get a job, while others, are hired because of skill or more liberal social norms at company A. For others, support is not available and some might struggle when they get laid off and have to move to company B with more rigid social norms.
The number 80; it doesn't feel that odd, if you look at all the pro's and cons, but I hear that number floating around too much without much proof to back those numbers up; but then again, as with all research, you can only make numbers from whomever participates.
Last year I conducted a poll on this forum. And while the samplesize was small... I mean, I can't force people to participate, here are some numbers that came out.
About 44% said they were unemployed (all unemployment combined) while 37% said they had a job. It's nowhere the 80% of course, but even if almost half of the people on the spectrum have no job, that's a lot... even if half have a job. It's nowhere the rates for unemployment in general in developed countries (which is <8% in general if I'm correct).
https://www.aspiescentral.com/threads/the-aspiescentral-monthly-poll-march-2014.5642/