Right. I have boxes full of software I bought once, and I have the license to use it forever. But it's for Windows XP or older. I'd need emulators or WINE to run it now, and it's not really worth it. For some of it I even paid for a "lifetime" of updates, but that stops working out when they stop updating it. I apparently live a lot longer than 90s and 2000s software companies. Just let me pay for major versions again with a guarantee of updates for X years, and price it according to those expectations.

37Signals is the company that made Basecamp, and they talk about hosting the software yourself, so presumably they are writing web software that would often be SaaS and letting you host it. So it's great that you'll be able to get it for one time purchase. But it definitely needs updates, as libraries change versions, new security flaws are uncovered, obviously for bugs, etc. Buying web application software is only as useful as the length of the updates included. Them providing the source is better, but since that's not open source exactly a community couldn't really work together to continue updates themselves.