You're misunderstanding. See the sibling thread where p_l says that this problem has been resolved, and any further occurrence would be treated as a bug. Setting the quota is only done now to reduce fragmentation (ZFS's fragmentation avoidance requires sufficient free space to be effective).
According to rincebrain, the "disk too full to delete files" was fixed "shortly after the fork" which means "shortly after 2012." My information was quite out of date.