I'm not sure the NTMA who offer state savings are regarded as a bank. I cant see anywhere if they are regulated by the central bank. If not, they might not need to follow same regulations.
For any banks in Ireland that do not give the notice, they sometimes have some notice element built into their accounts like BOI reg savers I think. This way they might not need to provide notice.
Also, there is a possibility that accounts are offered on an issue basis so that existing customers are still on the old rate but accounts opened going forward are on the new lower rate.
Another option could be to personally notify customers maybe through email or online banking. This would cover off existing customers.
I do agree though, some of the rate cuts that are put in place immediately seem to go against the regulations.