Like rg4619 said, the 2 episode/disk format itself is not uncommon, but that's generally limited to short 1-cours series (like Haruhi). For a 24 episode series, 3 episode/disk is the more common scheme.
Having to buy 12 DVDs (especially if the price remains "normal" in the 5,000-6,000 yen range) to collect the whole series is quite a hard task even for the most devoted otakus.
One thing to realize is that many Japanese otakus watch their animes recorded (for many of them, it's impossible to stay up until the wee hours just to catch their show), so for a lot of them, buying the DVDs is simply another act of collection, as well as a way of supporting the makers. So for some, it doesn't really matter how many episodes there are on a disk. The more important question would be "how many people out there are willing to pony up their money to collect this?"
Simply put, it's milking. But hey, without it we wouldn't have animes.
Just think of it as an investment towards making CLANNAD better or something.
