Sites do this because 90% of users don’t leave over modal popups and doing it increases engagement in enough cases to warrant keeping it.
It’s completely reasonable for a product to advertise for a newer version. How else would you know there’s a new version that you might actually decide you want to buy? And you don’t have to buy it.
> It’s completely reasonable for a product to advertise for a newer version.
No argument from me there. A notice on the splash screen, even a tool tip at start-up would work fine, but it was a full screen advertisement, several minutes after start-up, which stopped playback (!) without warning. These interruptions are what I find completely unacceptable, and I believe they stem from fundamentally misunderstanding what the user is there for, or outright disrespect.
Notice on the splash screen, a tool tip at start up, a popup at startup (anyone remembers "Tip of the day" dialogs?), a modeline/status bar (like e.g. IntelliJ IDEA does), ... there are plenty of well-established UI patterns for placing such information unobtrusively. As you said, firing up a modal in the middle of your work is unacceptable, and outright disrespectful.
It’s completely reasonable for a product to advertise for a newer version. How else would you know there’s a new version that you might actually decide you want to buy? And you don’t have to buy it.