same with variableRowHeight.
Correct, the mx:List and s:List components are two separate components and don't always have the exact same APIs. Most of the time the same functionality exists in both controls, but they may have slightly different names. I believe the latest Flex 4/ActionScript 3.0 Language Reference is posted at http://help.adobe.com/en_US/FlashPlatform/beta/reference/actionscript/3/ and should list which properties/methods/styles are supported by each component.
As for your dataTip question, this may work for you: http://blog.flexexamples.com/2009/08/15/creating-data-tips-on-a-spark-list-control-in-flex -4/
Not 100% certain about the variable row height, but I can take a look.