In the old version, it approached infinite cost at max allocation. I thought in the old videos explaining the allocation, it said that there was a disincentive to buying more than needed. However, in explaining the new market based system, the post says there was an incentive to buy more than needed in the old system... i.e. exactly the opposite. What changed? Am I misremembering the old videos?
According to Dan Larimer's Medium post, they determined that users who acquired cheap RAM would have no incentive to release it if they weren't using it since there was no financial incentive to do so. By switching to a market-based approach, holders of staked RAM are now incentive to "sell" any RAM they aren't using on the market, which makes it available to users who need it.
The downside to this approach is that those who buy RAM cheaply have no financial incentive to free RAM for other users after it gets more congested. Under Dawn 4.0 the system contract now buys and sells RAM allocations at prevailing market prices. ... Overall this will result in the market balancing the supply and demand for RAM over time.