A complete GCSE course amounts to 150 hours contact time. Throw in the sidetracks and disruptions inevitable in even a well-behaved class and you are looking at around 100 hours that actually count. That's not a lot of time: if you increase the breadth of the syllabus the depth of coverage must by necessity become paper-thin to compensate. If you spend that 100 hours covering a hundred specific cases the student walks away knowing nothing about how it all fits together and nothing that is still relevant come the next version of Windows. Spend it on a smaller core of fundamentals and there's a chance the student actually retains something of value and that won't be obsolete in five years time.