So when the Mac Pro was released over a year and a half ago the graphics card on it was very good. However, some of you are complaining that a last-gen computer due for a refresh any month now has last-gen tech in it. Of course it does. Tautologically. Apple doesn't, or very rarely, update its tech mid-cycle in a product. It has yearly (or longer) refresh cycles and that's that. When the new Mac Pro comes out, then you'll see new high-end desktop graphics cards for the Mac, not before.
iMacs are all-in-ones. They should be compared to all-in-one performance and the new ones do pretty well in that regard. Laptops are laptops are laptops.
As for Mac graphics drivers being bad/causing problems - well a lot drivers seem to be crap on Windows 7 too. I can't even quantify the sheer number of threads there are complaining about bad AMD/Nvidia drivers causing problems. It's simply too huge.
The real bottom line is that Apple, at the moment, simply doesn't have a true gaming machine which is obviously perfect for that purpose - something with power in-between a Mac Pro and an iMac which is where such a gaming machine would fall. Macs are great as computers that also happen to play games in addition to doing whatever reason you bought the computer for. And in the past, given the offering for the Mac platforms, that was fine. However, given the popularity of gaming on iOS devices and increasing Mac sales, Apple has developed a base to start attracting more game development.
If they want to push the Mac as a gaming platform, and it remains unclear if they do, then Apple has a couple ways of doing so: 1) The rumored, smaller 3U form-factor refresh of the Mac Pro may better allow gaming variants as well as the traditional server/workstation variants. 2) Getting rid of the optical drive in the iMac and putting in a desktop GPU and required extra cooling. 3) Eventually more external GPUs will become available turning almost any computer with a thunderbolt connection into a pretty reasonable gaming rig. There may be a few issues with the number of memory channels, but those aren't huge by some Anandtech tests (will look for link), and can be ameliorated by later thunderbolt iterations.
Of course Apple will have to push/adopt newer OpenGL standards as well in its OS if it wants to pull business away from DirectX-Windows/XBox-only development. But even a lot of graphics intensive games on Windows don't even take advantage of the latest greatest DirectX version - e.g. The Witcher 2 is still DirectX 9, not 10 or 11. So getting the right form factor for games is a higher priority than adopting the latest OpenGL standards. OpenGL versus DirectX is a different battle and not one that Apple has full control over.