Well, my opinion is that they're doing what they can both to stay afloat and to survive (with "acceptable" profits). So just like any company we can expect decisions that aren't to our liking every now and then.
One of the most stable versions of PT was years ago when Macs were still beige and ugly. Things have in my opinion gone downhill somewhat when it comes to stability, but Digi/Avid bet (wisely) on DSP to drive their software and TDM locked them into a specific space. With Nuendo and others doing certain things way better the only way to move forward was to ditch TDM. What I see now is a software that is in general much better, but buggier.
From that perspective I think for some types of businesses it makes 100% sense to get onto PT11 with the new coding. If you're in post and have to output 60 minutes of content then you have to wait an hour for that to happen. For years we've been able to do that in Nuendo as fast as the computer can handle it. So for post that's a no-brainer. Get PT11 and save time. Time is money. And with that follows different hardware and now different pricing.
I think PT12 is probably worth it - again - for post people. The collaboration features will probably get highly used over time. $600 for those businesses just becomes "noise" added to billing to clients. If you're fully booked 50 weeks of the year, 40 hrs per week, it's only 30 cents per hour, for places that often charge $100's of dollars.
For anyone doing music or who is an independent engineer it's different though. I think the bar for when it becomes worthwhile is a bit higher. And I certainly would be a bit annoyed depending on what I currently owned. If I had PT 11 HD then I'd be annoyed that I'd be paying just as much as some with lesser versions.
BUT, since I only work on other studios' PT HD systems and personally own Nuendo the subscription (to license) is actually really neat for me. Because it allows me to do as much work as I can on Nuendo and when required I'll be able to just rent PT HD for the duration of the project, at which point I'll certainly charge that to the client one way or another.
So I don't think it's all bad this situation, but I agree that it's a bit annoying for some, and part of that may be that people will just have to get used to not upgrading as frequently and stick to their current version. But for most people I'm guessing if you can't produce good content with PT version 10 and up the problem probably isn't the software anyway.