Because it's not 'old'!
http://windows.microsoft.com/en-us/windows/products/lifecycle
Personally I'm not fond of W8 and until 8.1 I see no need to move from W7. I paid £180 for W7 Ultimate around 5 years ago and wouldn't like to get less than 5 years out of an OS, especially as Microsoft are supporting it for another 2 years.
Its old for me archelogical stuff.
Its like people who never buy new cloths or underwear due to they always bought the same stuff from the same shop.
only OS I used that works with blazingly fast speeds and without any hick ups is windows 8. its an awesome OS.
That DICE use windows 8 with 64 bit and 8gb ram just points to why windows 8 is the OS to go for BF4.
Naturally Microsoft could support windows 7 the same way but why would they do that? better to sell a new OS that works way better.
windows 8 has a ton of stuff written for it under the hood, much I suspect BF4 has also vs BF3.
The AMD consol involvement also would allow us a better PC gaming without the bad porting like elder scrolls type of ****.
now soon R200 x amd card is out so BF4 with 3gb ram will run as intended