Well - to be fair. You copied and pasted a small ladder that he made for a private boat to be mounted under a swim platform - then compared it to your large charter boat.
Wouldnt the more fair comparison be the ladders he made for large dive boats?
Either way - must be regional as like I said - Most dive boats have the T style up here. Im sure there is someone without it - but I dont know of any.
Maybe the regional thing has to do with the fact that there is more gear that a NE diver is likely wearing - who knows.
Out of the pictures he has on the website, the most fair comparison was the one listed - the rest of his ladders pictured go 4-5 feet out of the water, or are for small outboard engine boats in which the top platform is ridiculously small... that boat has the closest swim platform to the one on our boat...
theres always this one: