Before today, "broadband" was 4/1, but that didn't mean that 1.5m and 3m tiers were "against the law."
What this means is that if CenturyLink asks for financial assistance from the government to build out a new network to an underserved or rural area, the network they build must be capable of delivering 25/3.
As it happens, CenturyLink hasn't really been classifying its services as "broadband" for a while anyway. It's "High Speed Internet" and in the eyes of the telecoms, that's different.
Even if CenturyLink calls your connection "broadband" -- it already exists and was built during a time when that level of performance was considered acceptable for "broadband," and as such, nothing will be done about it until whenever CL was going to upgrade it anyway.