I don't know why it is done this way.
For the second question, it's not a matter of speed, IMHO. XML method requires vbphrases to be created for your options & menu title in admincp, not with modcp menus.
Although you can work without vbphrases in admincp, options and titles will be displayed like *[your_text]*, meaning you missed some vbphrases. See attached screenshot.
This is one of the two reasons why I've put this mod in the modcp section. I didn't want to play with xml and phrases for only one option in a menu. In a way, we can say it's faster to code for me, but code is not faster either way