Transaction is very complex math some of the reasons I prefer Jim Grey I interpret his work which Microsoft implemented in more than five places to developers like me.

So MySQL had a lot of work waiting for Peter Gulutzan like stored procedures and DRI and he was hired not very long ago so I still think it is easier to implement quantifiable mathematical Unit of work than the application layer version which require resource manager or provider to resolve the atomicity. That is not needed in the ANSI SQL version. And I am not saying there is DRI in MySQL either but both are complex tasks.