I've noticed this as well, the last couple of sales seemed to have less of the big AAA titles on extreme deals (the ~75% off range). How much of that is real, I dunno.
One thing is for damn sure, I have 365 games on steam and I'm in Noooo rush to go out and drop £30 at launch. Back when games made large leaps in quality every year £30 was a super easy justification, if you wanted eyeball orgasms you'd drop £30 on Crysis and £1000 on graphics hardware.
PC gaming has suffered the same fate console gaming did, fixed hardware stifles game innovation, without innovation why keep paying a premium for new games? The reason I (and many others) USED to put down £30 on launch for games was because generally speaking they were better than the games before them, now we see the same old CoD games rehashed constantly.
My strategy for the PS3 when I bought it about 3 years after launch was to simply buy games 2+ years old for no more than about £5, you weren't missing out on anything because in those 2 years nothing had appreciably changed.
Now everything is multi-platform and PCs have become stuck in the same upgrade cycle as the consoles despite sporting vastly superior hardware, so 2 things have happened.
1) I've stopped aggressively upgrading my PC
2) I've stopped buying new games.
Developers have a couple of options here, wait 2-3 years until the price naturally drops to £5 and have a 2-3 year delay on their ROI (return on investment) or put it on sale 6 months after launch and see the same value but 18 months sooner.
Indy games have made a massive comeback as well thanks to humble bundle, steam early access as well as kickstarter, I think that these naturally cheaper indy games are somewhat re-balancing the prices of the AAA counterparts. No one is going to sell an expensive to devleop AAA game at the same deal price as a cheap to develop indy game.