Thank you to everyone that has replied. I guess I should be prepared for this kind of drama when I have to upgrade an operating system, but I always end up irritated.
According to WAVES:
Why does my Waves Update Plan cost more than $300?
Once you confirm that you use all selected products on one computer at a time, all your non-overlapping Waves products (e.g. Platinum & SSL or Gold & Restoration, etc.) are capped at $300 per account per year.
If you choose to extend your Waves Update Plan for multiple products, the Waves Update Plan for all selected products will be extended by one year from the coverage end date of the product with the latest coverage end date.
This may cause other selected products to be extended by more than one year. Since the coverage costs $300 per year, Waves Update Plan fees will be higher than $300.
This may be easier to understand using an example. Let’s assume that today is March 1st, 2013.
Say you own two products: Diamond (current Waves Update Plan end date: September 2013), and SSL 4000 Collection (current Waves Update Plan end date: March 2013).
When extending Waves Update Plan for both of them, the new end date for both would be September 2014, which is a year from the product with the latest end date (Diamond, in this case.)
While Diamond coverage is extended by exactly one year, SSL coverage is extended by 1.5 years (from March 2013 to September 2014.)
In this case, we add the cost of 6 months of Waves Update Plan coverage for SSL 4000 Collection to the $300 cap.
So, the actual answer is that WAVES (unlike any other software developers out there at this time) wants $300 (or more) a year for you to play with their toys. I guess because their plug-ins will automatically get you a hit song or something that will create a lot of money for you to justify throwing them this gift every year.
For obvious reasons, I prefer to pay for my plug-ins on a one time per lifetime basis. Unless, of course, the developer comes along and greatly improves the plug-in. Then, I don't mind paying the developer a reasonable fee to upgrade to the new and improved version of the older plug-in. But a yearly fee is ridiculous for plug-ins.
Fortunately, most plug-in developers are very reasonable and don't try to hold their clients captive by introducing a licensing procedure that locks them out using plug-ins that they've already paid for. WAVES are not cheap to begin with. It hardly seems fair to require taxation year after year.