Due to an increasing amount of spam from hosts with invalid reverse DNS, the AHBL has instituted a policy of listing IPs with obviously invalid reverse DNS that are seen spamming.
As an example, the AHBL has seen an increased amount of spam from 188.8.131.52/16, assigned to "Vietnam Posts and Telecommunications". This entire range has reverse DNS of 'localhost' making it nearly impossible to identify what these hosts are (dynamic, static, servers, home users, etc).
We are not listing hosts with no reverse DNS - just invalid reverse.
Laziness is not an excuse - if you do not want your IP ranges to have reverse DNS, you shouldn't configure it as 'localhost', '.', or similar variations.