Pedometer++[1] has donations too — "Generous Tip of $1.29", "Massive Tip of $2.49", and "Amazing Tip of $6.49" (AU pricing).
According to the guidelines[2], "Apps that include the ability to make donations to recognized charitable organizations must be free", and "The collection of charitable donations must be done via a web site in Safari or an SMS". Nothing about donations not to a recognised organisation, so I'm guessing the rule is to avoid sticky laws regarding Apple's 30% non-donation slice.
