There won't be an internal card... there's no place to put it. And you're not any more left out than PPC owners... none of our computers are going to have internal upgrades either. As with most of the Windows PCs that had 802.11g built in on-board.
I know it is annoying, but it's just the way of things. Computers get feature upgrades. 802.11n is still ages away from ratification. But in any event, computers get new features. Every time you buy one, from any vendor, it is likely that the same vendor (and others) will release newer ones at a later time with additional capabilities. If it bothers you a lot, upgrade.
Otherwise, recognize that 802.11g is already faster than your internet connection, although it admittedly does not have the widest range.