It seems to me that this nicely illustrates a major problem with the current system. Here we have large blocks of IP space that, by their own rules, ARIN should take back. It all sounds nice on paper, but clearly there is a hole in the system whereby ARIN doesn't know and apparently has no way of figuring out that the space is no longer in use.
Or maybe it means that ARIN has priorities and recovering this space is low on the priority list. Anyway, you are wrong. ARIN does have a way of figuring out that the space is no longer in use. When some sucker buys the addresses and tries to use them, they will find out that they must first update ARIN's records. And when they do that, ARIN will learn about the deal. At that point, they have to justify their address space just like anyone else, and only get to keep the amount of address space which they can justify. The fact that there are few suckers around to buy these addresses means that these block have been kicking around for a long time. But if there is ever a crunch for IPv4 address space, you can bet that ARIN members will empower ARIN to act unilaterally and take back the space.
but the way things currently work it seems like if you can justify a block today, it's yours forever even if you stop actively using it.
You haven't read through ARIN's policies yet, have you? --Michael Dillon