The PC is not really a console, but a general computer.
Consoles are dedicated computer systems designed to run selected games and apps specifically designed for the console. As such they perform better than a PC would with simlar theretical hardware. Additionally consoles are standardised, with games designed for the console working (or atleast should) on all revisions of the console (in this case the DSi is a different console from the DS).
PCs on the otherhand have very little standardization and are general purpose. Software developed for PCs has to support different hardware configurations, different interface performances and even different opperating systems and functionality. On top of that there are always tasks running in the background which are not related to the game which have the potential to interfear with its performance. You can also easilly upgrade your PC to have better hardware or new opperating systems whereas a console can only be upgraded by buying one of a newer revision or newer design Thus why PC is not truely a console due to this flexibility.
On top of that all game consoles as far as I know use RISC based programming. All mac and windows opperating systems have to use CISC processors (Linux and other OS support RISC but generally are not in noticable demand). Additionally the architexture of game consoles is different from that of PCs, featuring different interface methods for less latency or syncronized components for graphics (Xbox 360 can get almost free AA unlike the PS3 due to the layout of its graphic processors).
The most noticable console for its difference in architexture is the wii. Although the weakest modern console (you are probably laughing at me for saying the wii) and not truely being from this generation, it is by far the most efficent of the consoles for what it does. It is extreemly optimized and not only can run games like your super mario galexy which are fun, but it does so far better than a PC would ever be able to do so.
The wii consumes a massive 17 watts of power on average. Less than some comercial household lights. Compared to my core i7 which alone consumes up to 130 watts and my geforce 275 GTX at 219 watts you already see how well the wii does its job and I have not even mentioned the other stuff my PC needs to work that chews power. Yes my PC runs SC2 on ultra with FPS higher than most people even in demanding custom maps but is made with technology 3 years newer than the wii but it can not run games at the same quality the wii does without chewing more power.
As you could see that comparision was stupid. I was comparing a PC with 2008-2009 technology brought in june 2009 to a wii console launched in 2006.
Now lets do something better, comparing my PC with its probably max 450 watt power consumption to a PS3. A PS3 can do a vast variety of stuff from playing blu-ray to your games like final fantasy with an unbelieveable 76 watt power consumtion (newest models). You will be very hard pushed to get a PC to do better for the same quality and at the same price. My PC cost 2000£, a bog standard PS3 costs no more than 300£ (probably less now).
There is no way you can call a PC a console due to the major differences in how they work. Software creation for a console is easy cause you know everyone has the same power of hardware down to even individual clock cycles where as in PCs you are often forced to use less efficent programming methods to occomidate for varience in hardware and even probability of better hardware (e.g. crysis).
All consoles are pretty ridged, with each one having clearly difined capabilities.
Where as PCs are highly customizable and flexible. Capable of performing a variety of tasks although have limitied efficency for a specific task. Yes my PC is able to do a lot more a lot better than a PS3 or 360, it does not do so more efficently.
Thus why its unfair to bring PC into this. Although I do agree to some degree that PCs are way superiour, they are not truely a console.
Its like compairing the queens gaurd to a guy able to choose any modern combat weapon in existance. Yes the guy will totally out class them with modern body armor and assault weapons but given the same task and gear he will not do as well as they do.