Yes, that's what I was wondering too.
IIRC when TR5 came out, didn't it have an improved audio engine? I think that was one of the selling points/driving force to upgrade back then.
As fas as the second question, IK ain't got no upgrade plan! Not that makes any sense to previous users. It's always the same: $x amount if you own any $99 product. Which in reality ain't that bad a deal.