Why are kitchen base cabinets usually screwed to the wall?
Nearly all the reasons you proposed for leaving them free are rare occurrences. (I'm not sure what "doing the stove" means. Cleaning?) On those occurrences it's fairly easy to pull a few 3" screws and do your business. 

To my mind they don't outweigh the reasons you offered for anchoring them, which mostly involve stability (safety) and a quality feel. Most folks want a sense of built-in cabinetry, rather than freestanding furniture, which can wobble and shift with use.