I think this decision is along the lines of thought someone mentioned above. Sony generally figures out who their majority users are and tries to screw over as many people who are not in that group as possible. This especially includes those who are not actually purchasing their hardware if possible (proprietary memory/DRM/etc...), but if they can prune down to their target audience without casualty, it makes it easier to market to that target. They made a clear mistake here, but you can see the logic they followed.
This is a gaming machine and they want gamers to use it. If you're a gamer and not a developer who might be interested in the otheros feature of the device, you are in the vast majority of the population using the system, and therefore not a threat. If you're a pure research group and you want to make these machines into a super computer, just don't upgrade. They've covered their bases on that front because you're not likely going to see the airforce decide they want to use their supercomputer for gaming. In fact, they would probably prefer to discourage their users from doing just that. This leaves the group I mentioned before. Anyone who is a gamer who would like to play with the hardware as well. This group can be split into two. Those who want to actively break into the system (a very small minority), and those who hold it as their right to play with the hardware (and it is their right since it was an advertised feature), which includes those who want to use the hardware for research projects on the side.
The mistake sony made was this. They slammed the door in the face of the community that prides itself on being able to work its way around the word proprietary. In an effort to "protect their IP" they have unleashed the streisand effect and pushed a lot of people who were in the developer's group directly into the "we have a right to hack this hardware group" and opened the flood gates to all their friends as well.
Where do I stand on this? I have my backwards compatible 80gb model. It works fine. I have played it about 3 times since April 1st last year and I have not paid a cent to Sony in that time. Before that, I probably clocked a good hundred hours on the console... on one game... in about 3 months... and was buying DLC within 15 minutes of release if I thought it looked interesting.
I'll vote with my wallet. Sony's rationalization of theft to prevent theft is deplorable.