On the Nestle Quick commercial when the kids say "Can we help you with your groceries?" watch some of the kids mouths and you can clearly see that they're lip-syncing "Ra ya ra ra ra ra ra?"
There's probably a reason for this. Also, it's probably like that actor's secret: when you're whispering on stage, you say 'apples oranges bananas' because all those words are plausible ones that get your lips moving.