They marketed the PS2 as a system that could:
1) Play PS3 games, including games with online functionality.
2) Use linux, and other OSes.
It is a Playstation 3. As such, one has a realistic expectation that "Playstation 3 compatible" software will run on it. Unlike the PC, Sony controls the hardware and licenses the software specifically to ensure such compatibility.
It had Other OS support. It was marketed as supporting it. People (in some cases) bought it specifically as a result of such support.
Here's the crux of the problem: They have made it impossible to actually use the device as it was marketed.
I have games that boast they have online support. Sony says they are PS3-compatible, and support networking (subject to the terms of the Playstation Network). They then use the PSN to force an upgrade which would disable the very functionality they sold me.
"Buy this PS3, get games, online functionality, and linux"
"Lose linux, or lose online functionality"
With forced firmware updates, it can get even worse. Newer PS3 games can require certain firmware versions to run.
"Buy this PS3 to get games, online functionality, and linux"
"Lose linux, or lose games, and online functionality"
Even if you accept the Playstation Network TOS changes, and feel that "it's their network, they can set whatever terms they want" - the PS3 was marketed as a dual-purpose device, and forced firmware changes would literally force you to choose between the two. That would be fine if it was sold that way, but it was not.