Programming the Emotion Engine isn't hard because it's a 128-bit processor. C is C, really. It also utilizes a fairly common MIPS core, similar to what you'd see in the PSone, PSP, and N64, albeit a few steps up (the EE is similar to a MIPS 5900).
The part that makes the PS2 so difficult to optimize for are the SPEs. It's pretty much be the equivalent of taking an old Pentium -- a fairly weak processor -- and attaching a handful of smaller, very fast processors that can only do SSE, to it, then telling you that in order to maximize the power of the chip you'd have to be sure to keep all of the processors fully utilized. It would be a nightmare.
Not only that, but the PS2 is all stream-based. As I'm sure you noticed, the PS2 doesn't have a whole lot of RAM of any sorts. As far as temporary storage goes, the PSP outclasses it by a fairly large margin. The PS2's strength, however, is in data streaming. Its architecture can push small amounts of data around at an incredible rate of speed. It's pretty much the opposite of PC design -- it deals with small amounts of data very efficiently rather than loading everything in memory and processing it slowly. Of course, that also requires a whole new approach when you're a programmer -- you have to keep the bus full at all times, otherwise you're not taking full advantage of the architecture.
So, really, the challenge of PS2 development isn't just the processor. Oh no, you wish you could be that lucky. The
entire system is a set of intricate challenges. That's why the late-release titles look so much better than the launch titles; it took forever for developers to learn the ropes (and from what I read, Sony's poor documentation didn't help matters). It's not like in the NES/SNES days where the later games looked better because developers were jamming new chips in the cartridge. No, in this case developers were finally learning how to deal with the system.
That said, the architecture is quite unique. I suggest reading up on it, it's very interesting.
Also how would modding my Wii be?
If you have a copy of Twilight Princess, an SD card, and want to play homebrew or PERFECTLY LEGITIMATE Wii channels,
about as easy as blinking your eyes.
If you want to play "backups," however, you'll still need a chip.