The benefit of getting a discount off any future extensions in the form of an upgrade discount is not a hidden feature of Super Suite, but rather an often publicized one. You can see that touted on the super suite details page as one of the features of that package.
Upgrade discounts are usually only given for new releases of an existing extension, and then only given to people that own the previous version, who "upgrade". A brand new product will only be considered an upgrade for people that have purchased the super suite. The concept is that since super suite includes "everything" then anything we create is technically an upgrade to that existing purchase. The amount of money spent is not analyzed when determining upgrade discounts, just the products purchased and whether this is actually an "upgrade" or a new offer.