The Poll is definitely biased
I think it was meant to be.
Sadly, Sony very often abandons their customers. Once you give them your money, they're off to get more money from other people. The most amazing recent example was their H9 camera, which came out with several bugs (for example a sports shooting mode that exposes pictures for 1/60 sec, to give a nice smear!
Luckily I didn't get that camera, though I was very tempted at first), these were never fixed, and then a new camera came out. On the other hand, they've been amazing me with the PS3, coming out with updates every 2 weeks. Maybe the competition is hard... And they certainly don't distinguish between the different hardware version of the PS3 - and they are very different! Much much more different than the 505 and the 500.
Of course Sony has a right to do whatever they want (until the lawmaker decides to interfere and give consumers rights that the free market can not provide them. I think in these cases of DRM, laws will have to be made at some point.) But most of us here represent consumers, users. And we can definitely complain about Sony's actions. For now, this is the only thing that can change their mind. We have a right to complain, loudly, and they have a right to ignore us. If we don't complain, you can be sure that they won't listen.
I also absolutely don't agree that "the 500 didn't change - it still does what it promised it would". The 500, or any bookreader is useless without content. Sony promised not just the content that was at the Connect store at the time, but much new content in the future. Now that a new format is available for all Sony readers but the 500, it is very likely that many books will be available only in the new, better format (will ebooks.com convert everything also to Sony's format? Will sony offer everything that ebooks offers on their connect site?) This is how sony is abandoning the 500 - I bet there will be no more new content very soon.
But, I have to say that I personally do not buy any DRM protected content from Sony anyway. I only buy books that I'll be able to read on any future reader I own. I simply do not trust Sony to allow me to transfer content to whatever reader is available in 10 years.
Has sony earned my trust? In no way! So, I have to say that I don't really care, Sony. You lost me some time ago. On DRM you really have to trust the company you buy from...