Believe it or not, even not too old (12.1T) IOS versions have issues
forwarding packets to .255 addresses.
Peter Dambier is right that his ISP is avoiding .255 and .0. Older MS
stacks (still plenty prevalent in the wild) get indigestion when
handed those final octets, notwithstanding the fact that they aren't
broadcast addresses on any network larger than a /24 or for one-ended
use like PPP... if you don't exclude them you'll end up putting
additional load on your help desk.