True Data Costs on Orange UK PAYG

Orange UK advertise their data costs as £4 per megabyte, but my
experiments suggest it's about twice that. After a very long and
painfully inefficient with Orange which you can have a chuckle about
here:

http://www.letsfixbritain.com/orangecustomerservice.htm

- I spoke to a technical guy who confirmed that actual costs are about
twice what Orange advertise because, in addition to the customer's
data, there is also:

1. Negotiation with intermediate servers on the internet
2. GPRS connection overhead
3. Recovery of data lost in the Orange network
4. Protocol overhead associated with managing transmission power

One thing he said which I can't believe is summarised in bulet 1 above.
He said that the overhead is not fixed because it depends on the
location in the internet you're moving data to - specifically - Orange
machines must "hand-shake" with intermediate servers - and you can't
know how many there are.

Now, I am assuming that GPRS is just a front-end to "The Internet" and
I know that "The Internet" takes care of itself - you just specify an
IP address and open a socket and the internet's intrinsic nature
handles what happens in between (DNS, routing, etc.). The internals are
not visible to end users and so Orange can't apply charges depending on
them.

If this is true, then their expert is talking twaddle.

Can anyone clarify this for me please?

Regardless, it seems unfair that the actual data costs are half what
Orange advertise, so I am taking action to get that put right.