John the reason is what was mentioned before... you can't retail something for more than what people are willing to pay.
Althought i do find it hard to believe that it'd be only $8 in Pakistan - somewhere closers to $20 i'd suspect.
But then its also to the supply&demand rule ...
if in the UK the population is say 100 people and in Pakistan its 10,000 people - now if you say that 75% of these people will buy Windows...
this means 75 Britains and 7,500 Indians
if you sell the software in the UK for $120, in pakistan you can make the exact same profit by charging only $12 ... you tag this concept into the fact of the cost-of-living which marketeers must always take into account, also the increased production costs (which for a big company like microsoft is something stupid like $4/copy)
simply economics really for those who've taken it
you always strive to make the most profit, and you don't always make the biggest profit but retailing at an extorsionate price.
The reason Windows is so expensive in the UK & US is because we're stupid enough to pay the prices ... if people refused to upgrade because of prices the priceing structure would be reworked to make people happy to again gain the biggest retail<->cost (profit)
its why alot of 3rd world countries will pay staff daily, because most would rather earn $1/day rather than $10/week - its seems better to be earning something everyday that you can spend right away than earning a bit more per week.