Because computers are so integral to how we as a society are evolving and functioning, and it's been pretty well stated elsewhere that men and women function/think quite differently, having software that powers society that's primarily written by-and-for 50% of the population is generally considered to be a detrimental thing.

This has been particularly evidenced in gaming where mixed development teams come up with games that appeal far more widely to the general audience than the typical all-male FPS product. (Yes, this is a crass generalisation, but I've spent several years as part of women in gaming movements/the IGDA WiG SIG and so on. Male dev teams just don't build stuff that women want to play, for the most part.)

As to the "I'd really like to be a computer programmer, but I can't" -- I'm aware this was a facetious remark, but it's far more insidious than that, really. When I was at school, I was good at maths and physics. I loved logic and 'decision maths' (which was basically algorithms; we studied things like the TSP). I played about with computers in my spare time, ran the school website, etc. What career was I advised to follow? Electrical engineering. Not computer science. I didn't even know you could study computer science until I was looking at university prospectuses for mathematics.

I've never thought "I wish I could $foo, but I can't because I'm a woman". But I have experienced problems due to my gender, on a day to day level it's more stuff like having people change the topic of conversation when you join in the circle, not being asked for your opinion, having to over-justify your techie-ness to 'fit in' which just ends up sounding horribly arrogant.. being deliberately excluded from some conversations, having people make all kinds of stupid assumptions which you then have to correct - no I don't do marketing, no my PhD wasn't in linguistics, and techie people hate being wrong.. not fitting into XL freebie t-shirts properly, not having healthy/vegetarian/non-beer options at CS events (ok guys may well have this too).. etc etc. I don't list career sabotage or anything here because I'm young, I've mostly been in academia and I'm now running a startup, so I'm lucky enough not to have had problems there. (Except when I worked in a computer shop and customers actually demanded to speak to "the computer man", but hey. Their stupidity, not mine.)

On the extreme flipside, and I don't see many women talking about this stuff: being female has been great for getting fast-track opportunities into stuff. e.g. being flown to America to attend the Austin Games Conference as part of a Microsoft women in computing initiative. I do feel sometimes that I was let into competitive schemes partly because I'm awesome and partly due to the fact I'm the only woman applying and it looks good if I get in because then they have Gender Balance. (note, I am awesome, but that little voice of "was it because I'm perfect for the position or was it because I'm a minority" never quite goes away. I imagine others have the same problem in different ways.) However, I'm pretty sure that compared to a male CS major with a similar background, I've had far more opportunity. I feel a little guilty about it, but if I didn't seize it, someone else would -- and I'm actively trying to help change the need for such things in the first place.