You're not alone in believing that, but that doesn't make it so. There are things they can try to figure out, and they do try. But, in the end, there's no way they can predict or control what your ISP or your mail client is going to do with a broadcast message.
A more effective solution would be a notification system built into the program. But then the complaint would be, "I started MC for the first time in 3 months—and was informed I missed a bargain!" Maybe a JRiver Upgrade Notifier running as a service...
I realize that nothing is going to be 100% reliable. In my case, I have NEVER received a new version notification notice from JRiver for any version of the software and rarely have issues receiving emails in general (or at least I haven't run into any cases where someone has complained about me not responding to a message that I never received, though they might eventually just assume I'm ignoring them...). I've always received my license key emails from JRiver without issue. Until tonight, I never realized that they sent out emails letting their users know a new version is available - without that knowledge, I never had any reason to believe I wasn't receiving other emails from them. I'm getting the impression that you're more interested in inserting some sarcasm into the conversation than in helping to find an actual solution to the problem. My hope in bringing this up is that they can attempt to investigate what's going on so the same thing won't happen when MC17 comes out.
At worst, my email provider (which is NOT my ISP - I use a separate service for my email and web hosting) or email client will flag a message as spam and put it into the spam folder. As I stated earlier, I check the spam folder regularly in case something important ends up there by mistake.
If JRiver would like to work with me offline to attempt to figure out what's going on, they know how to contact me and I'd be happy to provide them any information they may need to attempt to figure out what's going on.