Hello SD, hello everybody !
This is getting grumpy quite quickly ! (not helped by phrases like 'posh little jet' or whatever it was !)
I fly the Global Express, and I'm told (but I've not tried it out under lab conditions or anything..) but I'm told that it's possible to avoid an obstacle 7 feet from the aircraft windshield. Now I'm not sure about other jets, but you'd be surprised about their turning circles. However, this would take quite a bit of assymetric thrust and one of the brakes on. This would certainly throw debris right across the parking stands and possibly dig up the tarmac.
The residual thrust on the Global and GIV is just about enough for taxiing off from a flat ramp - as it is at Heathrow so I really don't think that this is too much of an issue (we're not talking about 777 engines after all), and as has been pointed out, the marshaller is there to see what's up behind otherwise there's not too much point in having them (Northolt's a good one - no aircraft for miles, nothing to bump into, rather boring really, but woe betide you if you start without the man in the white coat).
I've found the marshallers at LHR to be superb, and can't ever remember being nosed in there. But SD, please remember that 'us lot' are often one ship operations without the back up of immediately available technical support, without engineers, and well used by need to having to do everything ourselves. So, as Airking said, we have to protect against being boxed in because we don't usually have the contacts to find out who might be doing the boxing (if you'll excuse the crap English).
We do actually carry a tow bar on the Global (and we do on the GIV too) but in both cases it is a 10 minute job to get it out of the hell hole and a ten minute job to get it back (it's all in bits and fantastically inaccessible) - with the APU on it is a bit of a noisy and messy job. This is not ideal in pressed white shirt with up to a 13 hour sector ahead.
I kind of get the impression that you don't like biz jets, well that's ok, I don't like airliners too much, but don't judge us all by some short tempered little chap, you'll find them all over aviation it's just that you get to deal directly with them (I nearly said 'us' !) on biz jets.
Would be pleased to show you round ours sometime if you drop me a line
OGS