That must be why he turned himself in.
He was unable to give an actual physical address. Under the UK legal system you have to be bailed to an address. A PO box isn't enough. The chances of flight are high if the shit does hit the fan (compared to most people bailed) and (for example) the US decides to invoke the extradition treaty we signed in 2003 on the grounds of the espionage act 1917. That would be my move if I was a really stupid American FBI Director looking to alleviate political pressure from the senate and executive.
The other thing as well is that a rape charge generally doesn't get bail here, so he was already on shaky ground to start with.
Personally I think him being in the UK was a bad move to start with, this is probably the last country you want to be apprehended in if you're on the run from the states, just ask Gary McKinnon.
Wikileaks is in a very large part about influencing perception. Everything has a purpose. Again, someone who has been trekking around the globe because many government are after him is hardly not an escape risk.
Also, fleeing would make him look pretty bad in the eyes of many and I personally don't think he would be stupid enough to do so (that's not much of a guarantee, I'll give you that), since capture (see 'island') is almost inevitable.
I wonder if anybody has access to what those maximum penalties of the charges brought are (under Swedish law), and how they relate to being jailed pending an extradition hearing. That would be interesting because I read in one uncorroborated source that the punishment for the circumstances described is actually a fine, rather than jail time and it would seem that if that is really the case that any jail time at all (such as pending this hearing) would be excessive. If Assange fights extradition do they plan to hold him in custody during the whole time ? And if so how is that different from using this as a ploy to simply lock him up because he's a 'risk' ?
I wouldn't be willing to bet much money that he couldn't get out of the country if he were free and of a mind to flee.
The boats all leave from ports where there are customs inspections, crew and captains who would all not be too happy giving shelter to a fugitive, international airports need a pass by immigration and the chunnel does too.
Lots of illegals make it in and out of Britain but they don't start off as high profile fugitives.
I think you're giving him too much credit. The best he could probably do is go to ground inside England but even that is not that simple.