No, i was talking abou TG pro that, if I am not wrong, doesn't have paid upgrade every year.
Oh for some reason I thought you were implying iStats was cheap whereas TG Pro was expensive, but yes that is correct. Matter of fact it was free to upgrade from their Mac Store version "Temperature Gauge" to their retail version "TG Pro" (albeit they appear and function identically).
Apple blocked apps that use IOKit or at least certain parts of it from being updated in the Mac Store since its a low level API. So Tunabelly Software (TG Pro dev) thought it would just be easier and better to get everyone on TG Pro for ease of updates and use.
While the app is updated A LOT (today in fact) for bug fixes, tweaks, updates for new systems/components and aesthetically to blend with the current version of MacOS the feature set itself is similar to how it was 3+ years ago. Minor features have been added and other features streamlined but nothing I would refer to as worthy of a "paid upgrade".
Maybe iStat Menu brings more to the table with their updates to justify paid upgrades. I can say with a lot of confidence when it comes to a piece of software like this I don't like Djangos business practice. Not only do they charge for something you've already bought once but they can easily discontinue development for bugs/tweaks on older versions while continuing to develop the same piece of software. And forget about minor features being added to an older version once a new one is out.