It's a minor point, but the Nintendo Wii is actually fully compatible with Gamecube games; Gamecube controllers and memory cards can be used in conjunction with these games on the Wii.
In fact Nintendo has been doing backwards compatibility since a least 1998 when they released the Gameboy Color which is compatible with original Gameboy games. Since then the GBA, GBA SP, DS and DS Lite have all been backwards compatible to some degree.

I understand where you're coming from, but I would have to disagree. The Gameboy Color was much more than a repackaging of the existing Gameboy; for instance, the processor was twice as fast, it had four times as much memory, could address more rom from the game cartridges (therefore allowing larger games to be developed) and of course it added a colour screen.
http://en.wikipedia.org/wiki/Gameboy_Color
http://www.nintendoland.com/gameboy/tech.htm

lol , clock speed of 8Mhz FTW :p

Hell of a feature, too. If you collect console games, it gets annoying to swap out systems. When you don't have a lot of living space it's impractical to have a bunch of them (I live in a major city). Most of my systems are in storage. I'd rather buy the shovelware comps with old games or download them directly and sell my consoles on ebay. Let someone with oodles of space have them.
It's the same reason I got an ebook reader. I honestly don't have space for thick hardcover books.

I call pure shenanigans. I've heard multiple times from multiple Sony officials that BC is not coming back, ever. I highly doubt it ever will.
Also, the Slim does have an easily replacable hard drive, its actually "encouraged" according to a sony exec interview I read. On the Slim its actually supposed to be easier than on the original.

What about the Sega Genesis being fully BC with the Sega Master System?

But it wasn't fully compatible. Not only did it lack the functionality to run all SMS games (certain video mode restrictions and controller issues), it required an extra piece of adapter hardware just to get the cartridges/cards to plug into the Genesis. That extra hardware was virtually impossible to find outside of Japan and Europe, so for a large number of Genesis users, it effectively had zero backwards compatibility.

For those bitching about the Netflix thing:
http://www.roku.com/netflixplayer/default.aspx
$99.99 one time fee, no monthly fees, integrated wifi and all kinds of audio and video out, including HDMI. Boom.

I do think that backwards compatibility can be a great feature to have especially when you are doing something new, such as the Wii or you previous console didn't do as well but had great game never the less like the Gamecube. Also with the Wii, it was designed similarly to the Gamecube so it would be easier for developers to work on the Wii or transfer their GameCube projects onto the Wii without too many issues.
For the Gameboy Advance Sp and The Nintendo DS, it was great because the Hardware gave benefits, like back lighting and as with the Wii, the backwards compatibility provided a transition the DS. Also the backwards compatibility for the GBA was good as it was a on the go device and you didn't have to carry two systems with you. I believe that the DSi is also a transition console as it is an hardware upgrade that is like double of the DS. This is probably for the future when their will be DSi cart games or games that take advantage of the DSi's features.
Though at the exact same time, it does come off as selfish when people complain about Backwards compatibility because those people tend to give up their consoles and think of the next ones as upgrades.

Aren't there also perfectly functional PS2 emulators for PC?

are there? I haven't found any that are functional.

I know I had one at one stage that could at least load some PS2 evil dead game. Didn't run it very well but then the PC I was using was a piece of junk so I thought that was the reason

now that i agree on.
I like to have my things nicely sorted and neatly installed. *Yes i use straps and spirals to connect and attach the wires.* If you're not carefull you might get caught in a web of electrical wires. So i had a nintendo , sega 8bit , atari and a playstation at one time.
It was a real jungle. I got rid of all of them just because i hated switching connections all the time and it took a lot of room.
Now i've got em all on mame :)

PCSX2? Looking at the compatibility list, it says that about half the games in the database (~1100 out of ~2200) are playable (or rather, possible to play through to the end, though frame rate might be very low at times).