Great question
liati!
I find this feature very annoying as well!
I like having a working, dedicated "Recent Items" menu in the start menu, and even retaining the ability to have recent jump lists in the task bar, but I never use and do not like the application jump arrows in the start menu! They expand to take over my entire start menu (it is fairly compact).
Sure would be nice if there was a "disable start menu jump lists" option!