In the UK Windows 7 Pro 64-bit = £110
In the UK Windows 8.1 Pro 64-bit = £107
(Same online store quoted (scan.co.uk))
Bare in mind I've noticed Microsoft artificially keep Windows 7 prices high because it was actually selling. I think you'll find that's a load of rubbish to try and blame it on licensing prices...
When 7 came out I saw Vista Ultimate Licenses drop to below £80...
I don't know as this is correct, (and I have no way of finding out), but here goes anyway. Most items are paid for in advance by resellers, so the sell to public price is fixed by that. Unless of course, the dealer is willing to take a bath selling it at a loss, or the manufacturer has a ton of back stock that he's willing to get rid of at below expected ROI.
In the case of going from XP to Vista, the same dynamic existed as going from to Windows 7 to Windows 8 In other words, from a loved OS, to a loathed OS.
Plus, the discontinued OS was purchased by the dealer at $XX.xx, and to offset financing charges on money borrowed to purchase the old stock, the price needs to remain to same as when the OS was current.
New stock on the discon'd OS may not be available from M$, so the temptation is strong for a reseller to charge, "whatever the traffic will bear".
In the case of Vista and Windows 8, those failed launches could have forced M$ to drop its pants on the cost to dealers, exacerbating the price difference at retail.
I will say, that price difference doesn't seem to have reared its ugly head as much here in the US. Mostly I think, because Newegg, (at least in the US), laid in some heavy overstock on Windows 7. So, following Newegg's Email ads, I have seen Windows 7, priced lower than Windows 8, on several occasions.
To make a long story short, I think both M$, and its dealers together, have a hand in creating the pricing situation as it stands.