...So the question is, if the PS3 is so much like a PC now, what's the catch?...
Simple to answer, user-friendly and hassle-free. The pre-existing knowledge required to operate a current-generation console isn't much more then knowing to plug-in a few labeled cables, press the power button, and maybe insert a disc. In addition, the utilized operating systems are very-efficent and have interfaces that are very-easy to navigate.
Compare that to what computer users must know and-or eventually know to maintain and operate Windows XP, Windows Vista, or even MAC OS X. For instance, I have known people to obliterate their OS X installation by dragging the wrong icon into the trash. Watched Window users constantly wonder why their machines grow ever slower, because of unused files and registry entries confusing the system. Why devices suddenly stopped working, because a DRM has decided to zero-out registries or simply aggressively block it by all means. The list goes on and on. These problems are practically unknown to console users.
Of course, like any hardware driven device, consoles do have potential hardware life issues, and the XBOX 360 is by far no exception. However, typical users of other consoles enjoy some of the lowest defective unit rates in the industry, and rarely encounter problems (unless you threw your Wii-mote into your TV, or bashed your PS3 in with a flail-like controller).
It is true that consoles are indeed computers, however the hacking required to install an alternative OS onto a console is not a trivial task, and takes some serious knowledge of the hardware. Very, very few people are going to go to that much trouble to convert their console to use a general purpose OS.
I wouldn't entirely disagree, but the process isn't that much different then typical computer tasks of formating, insert image, and follow a few steps. The process isn't really difficult and believe most of the current installation procedures for PS3 Linux Distributions are less then twenty-steps now (some far less). Ultimately, it doesn't take a serious amount of knowledge of hardware, and if you learned how to install Windows on your PC, you can probably handle most of them as well.
Now if this was actually a greater focus for Sony and other software groups, we would likely see a much more user-friendly alternative. Where you could purchase a copy, insert the disc (or run downloaded file), it auto-installs, and you are ready to go.
EDIT: Just tested the Crysis demo. The menus and intro videos seem to be single threaded, but the game itself is multi threaded. It does in fact use all four cores, although not always equally. The CPU usage on all four is increased, although two or three will often be used more than the fourth. It will definitely use more than two cores when it needs to.
Presently Crysis doesn't benefit in performance from a quad-core or even a seriously over-clocked processor (gains less then one FPS), as its primary bottleneck is on the available video card(s).
Well, for one thing it's ready for future games and future software, which I'm sure will use more of it. Hardware manufacturers have made it very clear that computing is going multicore in the future, rather than cranking up the GHz.
The future seems to be shifting to Nvidia's CUDA (Tesla systems), because of it's incredible performance and cost-to-performance ratio, i.e. some big companies are already changing over. Many applications even when they do get their applications properly, but painfully multi-threaded, the gains are sometimes not as great as one would hope. In addition, most people barely find use out of two-cores, four-cores are hard to justify for most, and they want to be at eight-or-more cores before years end. I believe AMD and Intel have to address more fundamental issues, instead of throwing more cores at the problem.
Well, for one thing it's ready for future games and future software, which I'm sure will use more of it. Hardware manufacturers have made it very clear that computing is going multicore in the future, rather than cranking up the GHz.
For another, I do a bit of raytracing and photo manipulation as a hobby, and that's where the quad cores will really get maxed out.
Presently, Photoshop hit the ceiling with what they are going (willing) to accomplish with the current multi-core roadmaps set by AMD/Intel. The next editions of Photoshop will be based around Nvidia's CUDA GPU/GPGPU acceleration, which will bring about mind-boggling performance improvements. I anxiously await that edition, because I'm tired of how slow Photoshop runs without it.
However, didn't know of many people working with Ray-Tracing, and can easily see that taxing the best of systems. Good luck with that.