With the only console hardware announcement of the week, PSP Go, thoroughly leaked well ahead of the show, this year's E3 has had one obvious focus - peripherals. Each company had plenty of impressive software to show - there's little to choose between Sony and Microsoft on this front, and it would take a particularly churlish gamer to find too much fault even with Nintendo's line-up, which was far more crowd-pleasing than in previous years. But it wasn't software that was the real battleground in this year's briefings - it was accessories.

Blame Rock Band, Wii Fit and perhaps even SingStar. The runaway success of such heavily accessory-dependent games in recent years has overturned decades of standard industry logic which places strict limits on the success of almost any peripheral that's not bundled with the console itself. Suddenly, it seems that every living room is bristling with plastic instruments - and over 15 million households, it transpires, have hopped onto a Wii Fit board to try and shed a few pounds. At this rate, the Wii Fit balance board will surpass the peak installed base of the original Xbox or the GameCube by early next year.

Is it any wonder, then, that E3 teems with peripherals? Plastic gadgets and gizmos are everywhere. At Microsoft's conference alone, the first few presentations introduced us to new Rock Band Beatles instruments and a new skating controller, pimped onstage by Tony Hawk, which looks set to absolutely destroy carpets, polished floors and damage deposits up and down the country when it launches.

The award for the most ridiculous gadget of the show, of course, has to go to Nintendo's Wii Vitality Sensor, a peculiar thimble which, when placed on your finger, relays your pulse back to the console. I could see a more robust version of the hardware working as part of a future, more intensive product in the Wii Fit line; Nintendo boss Satoru Iwata, however, talked at some length about its potential as a relaxation device, hypothesising about games which measure your pulse to help you unwind or even fall asleep. Industry pundits have learned in recent years that betting against Nintendo's crazy ideas isn't a profitable business, but this one feels a little too absurd to work. On past form, it'll probably sell millions anyway.

Stars of the week, however, were a different class of peripheral - motion controllers. Here, Nintendo's game-changing influence on the entire industry has never been more clear, with both Microsoft and Sony devoting huge chunks of their presentations to showing off the technology which, they hope, will leapfrog Nintendo's Wiimote and beat the Kyoto-based firm at its own (hugely profitable) game.

Hundreds of thousands of words have already been expended on attempting to work out the relative advantages and disadvantages of Sony's motion sensor and Microsoft's Project Natal. Although both are squarely aimed at Nintendo's market share, these efforts have many significant differences. Sony has opted for a method which uses controllers; Microsoft's Natal eschews the controller entirely, favouring gestures and voice commands.

Leaving aside arguments over which technology is "better" - arguments largely prosecuted by people who haven't actually used either, and thus utterly pointless - there are a number of important commercial points which need to be made about the two different systems.

Firstly, Sony's copies something more than Nintendo's focus on motion control - it also copies a big chunk of Nintendo's design ethos and business strategy. The Sony approach is distinctly low-tech, relying on repurposing tried and tested technology for its ends. Its visual sensor is an EyeToy camera, which picks up the movements of glowing orbs on the controller - a technology which has been used for motion capture for years; its motion sensor seems likely to be a modified version of the Sixaxis technology which populates every PS3 joypad.

The ultimate effect of the system belies this technical simplicity - it is, by all accounts, accurate, flexible and robust. However, the advantage for Sony is one which companies like Apple and Nintendo have long understood - the technology is old, therefore it is reliable, readily available, well understood and, crucially, cheap.

By contrast, Microsoft's Project Natal is unquestionably cutting edge. Incorporating a camera with a bespoke sensor designed to map the 3D position of people and objects in the room, it's undeniably impressive. Its applications will differ from those of the Sony peripheral - Natal doesn't seem suited to tracking small, precise movements, but its ability to follow the motions of an entire body are unrivalled. In fact, Natal seems likely to live up to the initial description of Wii games - "jumping around your living room" - to an extent greater than any Wii or PS3 game will.

Natal certainly feels more futuristic than Sony's technology. It's got a brand new 3D sensor, and its software needs to calculate what all the complex human bodies in front of it are doing ...