Embassy Income statements under scrutiny due to misuse

It's always been suspected and hushed subject, many retirees who get the yearly certified letter, do not have the required amount available.
Until a few years ago I've always had to have the letter from the bank verifying my accounts, copies of my bankbooks and the embassy letter when applying for the yearly retirement visa. Only in the recent three years I did not have to show bank statements.
I'd always wondered why the immigration department required the certified letter from the embassy. Why didn't the immigration department provide that service and collect the fees?
Personally I prefer a monthly income verification method and monthly money transfers instead of transferring a yearly amount into a Thai bank. In the US my money is insured.