Flex 4 documentation article named "Selecting and modifying text" lists an finite final list of components that supports the selection:
RichEditableText
Label (Spark only)
TextInput (both MX and Spark)
TextArea (both MX and Spark)
RichTextEditor and all controls that have a TextArea as a subcomponent
This list does not include RichText component, but luckily with a new Text Layout Framework (TLF) [...]
