The menu item doesn't prepend setting_ or whatever like the system settings do, but indeed the menu object should have used the actual lexicon keys, corrected in the rtfm.
The actions will *usually* have the same ID, and I haven't noticed it being different anywhere, but I personally wouldn't rely on that as it isn't hardcoded like in Evo. You can use
$actionId = $modx->actions['resource/update']
or in the manager javascript
var actionId = MODx.actions['resource/update']
to get the proper ID.
Note that in 2.3 there are no more actions and instead the link would just be like..
manager/index.php?a=resource/update&id=340
or for 3PCs
manager/index.php?a=update&namespace=mycmp
The actions variables do still exist for backwards compatibility sakes (and any extras creating modActions in the build still create and can use them) but aren't used anymore by the core.