As I expected. It seems if you purchase a perpetual licenses by lunchtime Friday 17th August it will be maintained at the existing level. Software maintenance is set at 20%. So when your current software maintenance period expires, the XE annual fee will jump from $150 to $750 and XS will jumped from $0 to $150.
Buying XS today at $99 vs Monday at $750, is probably a worthwhile consideration if you have a small Xen project in the near future.