slhilly - for a start, training in teaching is often not like training in other industries. We have to keep up with the frequent changes in government policy etc, otherwise we would be accused of not having the interests of the chidlren at the forefront. When a new initiative is brought in, it makes far more sense for a school to train all its staff at the same time.
Google, Wiki etc seem to have convinced you that much of INSET time is spent doing individual professional development. I can assure you that in my experience, this is not the case. It is rare that a large school (and I teach in a secondary, so quite a lot of teaching and non teaching staff) gets the opportunity to meet together for longer than an hour to discuss, learn, practise and develop our skills. We have to be able to move forward together, and this simply isn't possible without spending chunks of INSET time together.
I don't think you can understand unless you've done it. I would not assume I can advise doctors, lawyers, bricklayers or bus drivers on how and when they should enage in professional development, as I have never been anything other than a teacher.
Unfortunately, much of what you, and various other posters on MN think, is that schools should organise themselves to cause as little inconvenience to working parents as possible. Well guess what, I'm a working parent too, with bugger all flexibility about when I take my holidays. When I'm at work, doing an INSET day, my DTDs are invariably off school, so I have to sort out childcare. As many other posts have pointed out, this is just the way it is when you choose to have a child.
You may accuse me of missing your point, but I'm afraid I consider your "point" to be an ill-informed one.