OK...the 12volt engine and genset alternators don't need 3-stage regulators because they are charging starting batteries not deep cycle batteries.
Deep cycle batteries require a 3 stage (bulk, absorption, float) charging system. Every deep cycle battery manufacturer will tell you that.
A standard or automotive engine alternator regulator, like Leece Neville, charges at 28.8V constantly and the current falls off as the batteries charge up. The voltage never drops below 28.8V when the batteries are charged and this is a big problem if one runs the engine for a long time...like all day motoring.
28.8V constantly on your deep cycle bank will eventually kill the deep cycle batteries.
IF you only ever motor for a few hours at a time and not every day, then this is not such an issue.
3-stage alternator regulators are not a "scam", they are the best way to look after your deep cycle batteries.