Here's the thing about purchasing software, if you don't need the new features (or support), you don't have to renew.
I purchased WHMCS back in 2005 I guess is when they started (I'm sure I used something before them). Anyway, I believe my price was $49 or something.
The software has come a LONG way since then. It's not fair that they can't make any more money given that I purchased it so long ago.
I don't believe in the one payment system. There's no reason to advance the software when it's a one and done.
I also have an Owned Licence for Kayako - The EVERYTHING version from back in 2004/2005 also. I want to say I spent $50 on that too, unlimited users etc, LIFETIME updates (even today). The last "purchase" price I saw for it was in excess of $1,000, but it looks like they've now gone to a monthly only system.
Photoshop is the same way. I pay $50/month for ALL Adobe software, regular updates, *OR* I can use my Photoshop 2.0 from 10+ years ago - I think the last suite I purchased was near $3k before moving to the monthly model.