So Openal is being developed by Creative . So it can do better sound than EAX? Do Sound Cards benefit from it in any way ?
well - for the most part yes, but only because OpenAL is way more flexible than EAX is. OpenAL includes support for EAX 4HD, so if you have a soundcard that supports OpenAL, and you're running a game with native OpenAL support, you can run EAX 4. And seeing as how within the API, EAX is an extension, game devs have access to more audio procedures with OpenAL than they do EAX.
Sound cards can benefit from OpenAL, if the game natively supports it - but in the sense that it allows the game engine to use audio hardware acceleration directly, instead of having to rely on EAX or DirectSound calls which then have to be passed to the OS to interact with the hardware; OpenAL installs at the kernel level, instead of the user level; it offers better support across a range of hardware manufacturers, game developers, and operating systems, and also allows for the DirectSound/Vista workaround with Creative cards.
But, that's also not to say EAX is going dead anytime soon - Creative re-invents the wheel with each new major hardware series released. EAX was going strong for a long while, and still is, there have been a good 10-20 major games released this year so far that support EAX; but with Vista hovering over the industry, we'll start to see more support for OpenAL than EAX (seeing as how EAX is worthless in Vista) . . . and considering Creative is the major developer behing OpenAL right now, I think we'll start seeing EAX merged entirelly with the OpenAL project . . . EAX won't die, it'll just be re-incarnated.
Such is the way of Creative.