If it were just about HAL's and the advantages of them I'd agree but there's more to it than that.
It also allows MS and NVidia/AMD to control their market. We perceive that they are competing on performance but are they really?
The rate the gfx card market turns over would be any manufacturers dream. That isn't by accident and the ability to control it via software has been witnessed time and time again. Like Crysis being advertised as needing DX10 for full effects, of course you just turn on full effects in DX 9.
I prefer the old days like the Amiga where you had a hardware abstraction layer and could code "workbench" friendly graphics apps. But you could also fully take over the hardware and write directly to the gfx chipset, sqeezing out every last drop. Not for malicious purpose, but for performance.
It's a pity that ability has been stripped from us as a whole lot of great development ceased when low level hardware access was denied us.
There's too many people trying to control what you do and when on your PC these days. It isn't yours anymore.
Cheers,
Arkay.