Case in point, in the last few months my team has been expected to pick up 3 different programming languages/frameworks, none of which they have any prior experience with. A recruiter would sift them out on first pass. But they are experienced with similar tech, have access to colleagues who are already familiar - so they've been fine. How is that any different to a woman returning to work with a slightly outdated but fundamentally strong CV?
I agree with this - a lot of it is down to recruitment techniques. For example, the recruiting manager will write the spec. It will probably be ridiculously over-hopeful when it comes to essential, rather than desirable skills. It then goes to his manager, and possibly further up the tree, depending on how many levels there are between him (and yes, for tech jobs, it so very often is male all the way), and his director, or possibly higher, depending on the current rules on funding and sign-offs for headcount. Then it goes to HR to review and approve and publish to the world (and hopefully not mangle the spec in the process, which we have had before.)
Then the CVs come in - mostly through recruitment agents (I think these days, most places don't insist that CVs are only accepted through approved agents, but I have worked for a company which did that in the past.)
Recruitment agents will usually just do an string match on the named program languages/applications/hardware/operating system (depends on the particular job.) This will get rid of most of those who will have similar but not an exact match (this also goes both ways, like the the job I got forward for where they really wanted Veritas Cluster Server, and my experience is Veritas File System, which probably means I could blag it if I really wanted to and did a bit of cramming first, but it's not actually the same.) Then it goes to HR, and again, most of them aren't technical, so them reviewing CVs is matching the given skills again. And at that point, the recruiting manager will get to see the few CVs which are left (and then they apply their own prejudices and biases in chosing which to select for interview.)
This doesn't always happen - I've dealt with a couple of recruitment agents who clearly did know what they were talking about when it came to the technical terms, and that can also happen in HR, plus sometimes they'll sit down with the recruiting manager to discuss what's absolutely essential, what's nice to have, what's good solid background that would be transferrable and so on. Plus the recruiting manager will be not so set in their ways that they won't look at transferable skills either.
The other thing is cost - if you can bring someone in who already has experience with the required language or whatever, then they should be up and running more quickly, and won't need to spend time cross-training or at least, learning a new language. But I reckon training costs sort of balance out across employers over the years, or at least the good ones - they train some, who move on elsewhere, and get in others who were trained elsewhere.