There are some slight differences. I'm on a Star Class Promo fare to and from KIX later this month myself.
Firstly, you can pay Star Class normally (out of sales). These are light blue coloured when you select the fares on the JQ website. Standard Star Class rules apply, and you get business SCs and points.
Secondly, you can obtain Star Class by trying your luck with an ODU. I haven't done this before, but you pay up some cash and your Economy ticket gets upgraded into Star Class. I'm not sure which JQ Economy tickets (JetSaver Light, JetSaver (normal), JetFlex) actually are eligible, or all of them, nor do I have any idea how you can improve your chances of scoring an ODU. Yonks ago, I believe, an ODU meant you actually got business SCs and points, but now it seems (just like almost any other upgrade), you will only get the SCs and points of your originally paid ticket, i.e. if JetFlex, you get full economy SCs and points; if JetSaver then you get bupkis.
Thirdly, when JQ have a sale which also includes Star Class fares, they then "introduce" another kind of fare class called Promotional Star Class, which is denoted on the booking page as a dark orange colour with a white star in the corner of the box (rather than the standard light blue colour). This is exactly the same as a Star Class fare in every way, except there are more restrictions on the Promo fare, e.g. refundability and flight detail changes are heavily restricted. Otherwise, there is no real other difference; you get business SCs and points.