Some of that looks pretty tame to me actually and I'd be happy to handle it on a hardtail - £400 or £3000. But no, in general, not that sort of level of stuff. I'd look at full-sus if I was going that way, probably.
cjb - you are perfectly entitled to your opinion, of course, but you do seem to be blinded by the pound-sign-trick that eminates not just through cycling but most hobbies that require specific equipment. As Zoiders said, specifically with bikes, more money generally gets you lighter stuff, not necessarily stronger. Sure, a £3500 bike, kitted with £400 forks, will handle better, be lighter and probably last longer than one half the price - or a quarter of the price - but to imply, as you are, that you need to spend that money (OK, maybe not £3500, but certainly more than £400) just to even get off a road is somewhat ridiculous.
It's like saying that, to cycle up the classic mountain passes in the Alps and Pyrenees, you need a full carbon bike that cost at least £1500. Anything under that simply won't get you up them. Which is rubbish - you could cycle up those passes on a steel touring bike loaded with panniers - it won't be as easy or perhaps as comfortable, but it's still possible. Just because manufacturers make these high-end products and components doesn't mean they're essential for the job - nice to have, sure, if you want to pay for them (and I do on occasion), but certainly not essential.
Off-road is different, of course, but to suggest a £400 machine is unsuitable simply because of its cost (you haven't actually said yet what it is about the cheaper bikes you're so concerned about - do you think a <£400 suspension fork is going to collapse if it hits a tree root?) if quite frankly naive.
