I think it has as much to do with standardization as ease of use. This way, if there are multiple experts, they don't each do it their own way.
Plus, it gives a degree of reliability to those using the packages, which is something you can't necessarily count on in Haskell right now.
That said, it might be the case that removing the responsibility of versioning from experts would make them less concerned about the ramifications, and less likely to notice when they make a change like this one (well not this one exactly, but one similar but more reasonable).
You really do need tests in addition to static analysis to be sure of these things.
[0]: http://www.loper-os.org/?p=861