the limitation does still exist. There are two things:
a) there is a difference between the Live Parameter System and Max Presets. Live Parameters are those values that can be modulated from Live (in example from within a clip or via the Max Live-API from another Max For Live device). for standard max objects autopattr will still find the them and save the presets but the values of all non live.xxx ui objects won't be visible for Live. In order to expose them you will need individual pattr objects as mentioned in the docs.
b) the reason why your live.numboxes can be exposed as parameters to live is because all live.xxx ui objects have by default the ability to be exposed to Live as parameter to live. You can activate them by simply choosing a modulation type in the inspector. Definitions for the different Modulation type are described inside this tutorial:
In this particular case I am not interested in modulating or automating the parameters, I am only interested in the possibility of saving a bunch of Max presets in a single Live device preset (the one you can save clicking on the tiny floppy icon in the upper right of the device window).
However you put me in the right direction: I misunderstood the docs, the pattr object is only necessary for registering the standard max objects with the parameter system, not to memorize and save Max presets.