Thanks for using the LotusLive Notes forum.
You are certainly correct in your summary. Instant Messaging is a feature of the LotusLive Notes client, but not in the LotusLive Notes Web client. The Sametime client can be installed for use with LotusLive Notes web.
Instant Messaging is a feature that is planned for LotusLive Notes Web. It is being investigated and worked heavily, but unfortunately we cannot commit to specifics at this time.