You know, whereas blocking the range in a lot of cases will hit sites hosted on the same server; it won't ALWAYS do that... You could actually block legit users (assuming that the block is actually used by other users and not just a server farm).
For example, I own IP's .15x, but I don't own anything other than that, they're owned by other users in my datacenter; now if i where to just block the whole class C, that'd hit a load of users who wouldn't be ones even associated with the org...
