I'm not a designer, but I use Illustrator often. I just bought Illustrator 10 for about $100 and it more than meets my needs. How many truly relevant new features can really be added to a vector drawing program?
I think you are right regarding the Illustrator issue though, I still have CS2 on my machine and I don't think there has been a noticable change up to CS5, that might be why its one of the cheaper subscriptions??
Photoshop is constantly changing in my eyes, they introduced the 3d tool 2 versions ago and I would imagine they spend the next few versions perfecting it. At that point they introduce another big feature.
I think a lot of the time the upgrades are non essential though and are just a money spinner. Apple do it though once a year but they only charge a nominal fee for their software. Microsoft do it every few years but they are a rip off.
I know that if I was a Freelancer and my software was not covered by the company then I would be more inclined to go down this route than downloading it. I don't know many freelancers that start up and can afford the latest version of any of Adobe's products. They are the industry standard and they have people by the balls, this way they can try to get potential illegal downloaders interested.