I guess what happens is that individuals vote with their wallets. If some courier loses your parcel, damages your parcel or their customers service sucks when trying to get compo, then that individual will move on to a different courier. It seems poor service is not going to be addressed by legislation, as has been achieved with the likes of Wonga.
It seems to be down to the individual to use a different courier. But until 1000's and 1000's of disgruntled customers all vote with their wallets, i doubt we'll get better service